diff --git a/src/output.cpp b/src/output.cpp
index 3dac0238b..2a7a1c6a6 100644
--- a/src/output.cpp
+++ b/src/output.cpp
@@ -299,7 +299,7 @@ write_tallies()
   // Loop over each tally.
   for (auto i_tally = 0; i_tally < model::tallies.size(); ++i_tally) {
     const auto& tally {*model::tallies[i_tally]};
-    auto results = tally_results(i_tally+1);
+    auto results = tally_results(i_tally);
     // TODO: get this directly from the tally object when it's been translated
     int32_t n_realizations;
     auto err = openmc_tally_get_n_realizations(i_tally+1, &n_realizations);
diff --git a/src/simulation.cpp b/src/simulation.cpp
index 978f57e0f..89ad54c4f 100644
--- a/src/simulation.cpp
+++ b/src/simulation.cpp
@@ -546,7 +546,7 @@ void calculate_work()
 #ifdef OPENMC_MPI
 void broadcast_results() {
   // Broadcast tally results so that each process has access to results
-  for (int i = 1; i <= n_tallies; ++i) {
+  for (int i = 0; i < n_tallies; ++i) {
     // Create a new datatype that consists of all values for a given filter
     // bin and then use that to broadcast. This is done to minimize the
     // chance of the 'count' argument of MPI_BCAST exceeding 2**31
diff --git a/src/state_point.cpp b/src/state_point.cpp
index a808e3ef5..aa1fc0e65 100644
--- a/src/state_point.cpp
+++ b/src/state_point.cpp
@@ -249,10 +249,11 @@ void write_tally_results_nr(hid_t file_id)
     write_dataset(file_id, "global_tallies", gt);
   }
 
-  for (int i = 1; i <= n_tallies; ++i) {
+  for (int i = 0; i < n_tallies; ++i) {
     // Skip any tallies that are not active
     bool active;
-    openmc_tally_get_active(i, &active);
+    // TODO: off-by-one
+    openmc_tally_get_active(i+1, &active);
     if (!active) continue;
 
     if (mpi::master && !object_exists(file_id, "tallies_present")) {
@@ -270,7 +271,8 @@ void write_tally_results_nr(hid_t file_id)
     if (mpi::master) {
       // Open group for tally
       int id;
-      openmc_tally_get_id(i, &id);
+      // TODO: off-by-one
+      openmc_tally_get_id(i+1, &id);
       std::string groupname {"tally " + std::to_string(id)};
       hid_t tally_group = open_group(tallies_group, groupname.c_str());
 
diff --git a/src/tallies/derivative.cpp b/src/tallies/derivative.cpp
index b0ff83ea3..df65b0751 100644
--- a/src/tallies/derivative.cpp
+++ b/src/tallies/derivative.cpp
@@ -110,8 +110,7 @@ void
 apply_derivative_to_score(Particle* p, int i_tally, int i_nuclide,
   double atom_density, int score_bin, double* score)
 {
-  //TODO: off-by-one
-  const Tally& tally {*model::tallies[i_tally-1]};
+  const Tally& tally {*model::tallies[i_tally]};
 
   if (*score == 0) return;
 
diff --git a/src/tallies/tally.F90 b/src/tallies/tally.F90
index d4fb20455..6d2c83ab2 100644
--- a/src/tallies/tally.F90
+++ b/src/tallies/tally.F90
@@ -152,7 +152,7 @@ contains
 
     ! Accumulate results for each tally
     do i = 1, active_tallies_size()
-      call tallies(active_tallies_data(i)) % obj % accumulate()
+      call tallies(active_tallies_data(i)+1) % obj % accumulate()
     end do
 
   end subroutine accumulate_tallies
diff --git a/src/tallies/tally.cpp b/src/tallies/tally.cpp
index 5343b7cec..5f6287b89 100644
--- a/src/tallies/tally.cpp
+++ b/src/tallies/tally.cpp
@@ -233,12 +233,12 @@ Tally::set_filters(const int32_t filter_indices[], int n)
     if (i_filt < 0 || i_filt >= model::tally_filters.size())
       throw std::out_of_range("Index in tally filter array out of bounds.");
 
-    //TODO: off-by-one on each index
+    // Keep track of indices for special filters.
     const auto* filt = model::tally_filters[i_filt].get();
     if (dynamic_cast<const EnergyoutFilter*>(filt)) {
-      energyout_filter_ = i + 1;
+      energyout_filter_ = i;
     } else if (dynamic_cast<const DelayedGroupFilter*>(filt)) {
-      delayedgroup_filter_ = i + 1;
+      delayedgroup_filter_ = i;
     }
   }
 
@@ -274,7 +274,6 @@ Tally::set_scores(std::vector<std::string> scores)
 
   // Check for the presence of certain restrictive filters.
   bool energyout_present = energyout_filter_ != C_NONE;
-  //bool delayedgroup_present = false;
   bool legendre_present = false;
   bool cell_present = false;
   bool cellfrom_present = false;
@@ -531,7 +530,8 @@ adaptor_type<3> tally_results(int idx)
   // Get pointer to tally results
   double* results;
   std::array<std::size_t, 3> shape;
-  openmc_tally_results(idx, &results, shape.data());
+  // TODO: off-by-one
+  openmc_tally_results(idx+1, &results, shape.data());
 
   // Adapt array into xtensor with no ownership
   std::size_t size {shape[0] * shape[1] * shape[2]};
@@ -541,10 +541,11 @@ adaptor_type<3> tally_results(int idx)
 #ifdef OPENMC_MPI
 void reduce_tally_results()
 {
-  for (int i = 1; i <= n_tallies; ++i) {
+  for (int i = 0; i < n_tallies; ++i) {
     // Skip any tallies that are not active
     bool active;
-    openmc_tally_get_active(i, &active);
+    // TODO: off-by-one
+    openmc_tally_get_active(i+1, &active);
     if (!active) continue;
 
     // Get view of accumulated tally values
@@ -605,33 +606,32 @@ setup_active_tallies_c()
   model::active_meshsurf_tallies.clear();
   model::active_surface_tallies.clear();
 
-  //TODO: off-by-one all through here
   for (auto i = 0; i < model::tallies.size(); ++i) {
     const auto& tally {*model::tallies[i]};
 
     if (tally.active_) {
-      model::active_tallies.push_back(i + 1);
+      model::active_tallies.push_back(i);
       switch (tally.type_) {
 
       case TALLY_VOLUME:
         switch (tally.estimator_) {
           case ESTIMATOR_ANALOG:
-            model::active_analog_tallies.push_back(i + 1);
+            model::active_analog_tallies.push_back(i);
             break;
           case ESTIMATOR_TRACKLENGTH:
-            model::active_tracklength_tallies.push_back(i + 1);
+            model::active_tracklength_tallies.push_back(i);
             break;
           case ESTIMATOR_COLLISION:
-            model::active_collision_tallies.push_back(i + 1);
+            model::active_collision_tallies.push_back(i);
         }
         break;
 
       case TALLY_MESH_SURFACE:
-        model::active_meshsurf_tallies.push_back(i + 1);
+        model::active_meshsurf_tallies.push_back(i);
         break;
 
       case TALLY_SURFACE:
-        model::active_surface_tallies.push_back(i + 1);
+        model::active_surface_tallies.push_back(i);
       }
     }
   }
@@ -916,9 +916,6 @@ extern "C" {
   int tally_get_energyout_filter_c(Tally* tally)
   {return tally->energyout_filter_;}
 
-  int tally_get_delayedgroup_filter_c(Tally* tally)
-  {return tally->delayedgroup_filter_;}
-
   void tally_set_scores(Tally* tally, pugi::xml_node* node)
   {tally->set_scores(*node);}
 
diff --git a/src/tallies/tally_header.F90 b/src/tallies/tally_header.F90
index d857a726e..8784b63b4 100644
--- a/src/tallies/tally_header.F90
+++ b/src/tallies/tally_header.F90
@@ -130,7 +130,6 @@ module tally_header
     procedure :: n_nuclide_bins => tally_get_n_nuclide_bins
     procedure :: nuclide_bins => tally_get_nuclide_bins
     procedure :: energyout_filter => tally_get_energyout_filter
-    procedure :: delayedgroup_filter => tally_get_delayedgroup_filter
     procedure :: deriv => tally_get_deriv
     procedure :: set_deriv => tally_set_deriv
   end type TallyObject
@@ -506,19 +505,6 @@ contains
     filt = tally_get_energyout_filter_c(this % ptr)
   end function
 
-  function tally_get_delayedgroup_filter(this) result(filt)
-    class(TallyObject) :: this
-    integer(C_INT) :: filt
-    interface
-      function tally_get_delayedgroup_filter_c(tally) result(filt) bind(C)
-        import C_PTR, C_INT
-        type(C_PTR), value :: tally
-        integer(C_INT) :: filt
-      end function
-    end interface
-    filt = tally_get_delayedgroup_filter_c(this % ptr)
-  end function
-
   function tally_get_deriv(this) result(deriv)
     class(TallyObject) :: this
     integer(C_INT) :: deriv
diff --git a/src/tallies/tally_scoring.cpp b/src/tallies/tally_scoring.cpp
index 991b4cc27..770ab7868 100644
--- a/src/tallies/tally_scoring.cpp
+++ b/src/tallies/tally_scoring.cpp
@@ -146,9 +146,8 @@ void
 score_fission_delayed_dg(int i_tally, int d_bin, double score, int score_index)
 {
   // Save the original delayed group bin
-  //TODO: off-by-one
-  const Tally& tally {*model::tallies[i_tally-1]};
-  auto i_filt = tally.filters(tally.delayedgroup_filter_-1);
+  const Tally& tally {*model::tallies[i_tally]};
+  auto i_filt = tally.filters(tally.delayedgroup_filter_);
   auto& dg_match {simulation::filter_matches[i_filt]};
   auto i_bin = dg_match.i_bin_;
   auto original_bin = dg_match.bins_[i_bin-1];
@@ -182,10 +181,9 @@ score_fission_delayed_dg(int i_tally, int d_bin, double score, int score_index)
 void
 score_fission_eout(Particle* p, int i_tally, int i_score, int score_bin)
 {
-  //TODO: off-by-one
-  const Tally& tally {*model::tallies[i_tally-1]};
+  const Tally& tally {*model::tallies[i_tally]};
   auto results = tally_results(i_tally);
-  auto i_eout_filt = tally.filters()[tally.energyout_filter_-1];
+  auto i_eout_filt = tally.filters()[tally.energyout_filter_];
   auto i_bin = simulation::filter_matches[i_eout_filt].i_bin_;
   auto bin_energyout = simulation::filter_matches[i_eout_filt].bins_[i_bin-1];
 
@@ -268,7 +266,7 @@ score_fission_eout(Particle* p, int i_tally, int i_score, int score_bin)
     } else if (score_bin == SCORE_DELAYED_NU_FISSION && g != 0) {
 
       // Get the index of the delayed group filter
-      auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_-1];
+      auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_];
 
       // If the delayed group filter is present, tally to corresponding delayed
       // group bin if it exists
@@ -330,8 +328,7 @@ void
 score_general_ce(Particle* p, int i_tally, int start_index, int filter_index,
   int i_nuclide, double atom_density, double flux)
 {
-  //TODO: off-by-one
-  const Tally& tally {*model::tallies[i_tally-1]};
+  const Tally& tally {*model::tallies[i_tally]};
   auto results = tally_results(i_tally);
 
   // Get the pre-collision energy of the particle.
@@ -520,7 +517,7 @@ score_general_ce(Particle* p, int i_tally, int start_index, int filter_index,
       if (simulation::material_xs.absorption == 0) continue;
       if (tally.estimator_ == ESTIMATOR_ANALOG) {
         if (settings::survival_biasing || p->fission) {
-          if (tally.energyout_filter_ > 0) {
+          if (tally.energyout_filter_ != C_NONE) {
             // Fission has multiple outgoing neutrons so this helper function
             // is used to handle scoring the multiple filter bins.
             score_fission_eout(p, i_tally, score_index, score_bin);
@@ -563,7 +560,7 @@ score_general_ce(Particle* p, int i_tally, int start_index, int filter_index,
       if (simulation::material_xs.absorption == 0) continue;
       if (tally.estimator_ == ESTIMATOR_ANALOG) {
         if (settings::survival_biasing || p->fission) {
-          if (tally.energyout_filter_ > 0) {
+          if (tally.energyout_filter_ != C_NONE) {
             // Fission has multiple outgoing neutrons so this helper function
             // is used to handle scoring the multiple filter bins.
             score_fission_eout(p, i_tally, score_index, score_bin);
@@ -625,7 +622,7 @@ score_general_ce(Particle* p, int i_tally, int start_index, int filter_index,
       if (simulation::material_xs.absorption == 0) continue;
       if (tally.estimator_ == ESTIMATOR_ANALOG) {
         if (settings::survival_biasing || p->fission) {
-          if (tally.energyout_filter_ > 0) {
+          if (tally.energyout_filter_ != C_NONE) {
             // Fission has multiple outgoing neutrons so this helper function
             // is used to handle scoring the multiple filter bins.
             score_fission_eout(p, i_tally, score_index, score_bin);
@@ -638,8 +635,8 @@ score_general_ce(Particle* p, int i_tally, int start_index, int filter_index,
           // delayed-nu-fission
           if (simulation::micro_xs[p->event_nuclide-1].absorption > 0
             && data::nuclides[p->event_nuclide-1]->fissionable_) {
-            if (tally.delayedgroup_filter_ > 0) {
-              auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_-1];
+            if (tally.delayedgroup_filter_ != C_NONE) {
+              auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_];
               const DelayedGroupFilter& filt
                 {*dynamic_cast<DelayedGroupFilter*>(
                 model::tally_filters[i_dg_filt].get())};
@@ -676,8 +673,8 @@ score_general_ce(Particle* p, int i_tally, int start_index, int filter_index,
           // score. Loop over the neutrons produced from fission and check which
           // ones are delayed. If a delayed neutron is encountered, add its
           // contribution to the fission bank to the score.
-          if (tally.delayedgroup_filter_ > 0) {
-            auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_-1];
+          if (tally.delayedgroup_filter_ != C_NONE) {
+            auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_];
             const DelayedGroupFilter& filt
               {*dynamic_cast<DelayedGroupFilter*>(
               model::tally_filters[i_dg_filt].get())};
@@ -699,8 +696,8 @@ score_general_ce(Particle* p, int i_tally, int start_index, int filter_index,
         }
       } else {
         if (i_nuclide >= 0) {
-          if (tally.delayedgroup_filter_ > 0) {
-            auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_-1];
+          if (tally.delayedgroup_filter_ != C_NONE) {
+            auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_];
             const DelayedGroupFilter& filt
               {*dynamic_cast<DelayedGroupFilter*>(
               model::tally_filters[i_dg_filt].get())};
@@ -723,8 +720,8 @@ score_general_ce(Particle* p, int i_tally, int start_index, int filter_index,
               * atom_density * flux;
           }
         } else {
-          if (tally.delayedgroup_filter_ > 0) {
-            auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_-1];
+          if (tally.delayedgroup_filter_ != C_NONE) {
+            auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_];
             const DelayedGroupFilter& filt
               {*dynamic_cast<DelayedGroupFilter*>(
               model::tally_filters[i_dg_filt].get())};
@@ -776,8 +773,8 @@ score_general_ce(Particle* p, int i_tally, int start_index, int filter_index,
           if (simulation::micro_xs[p->event_nuclide-1].absorption > 0
             && nuc.fissionable_) {
             const auto& rxn {*nuc.fission_rx_[0]};
-            if (tally.delayedgroup_filter_ > 0) {
-              auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_-1];
+            if (tally.delayedgroup_filter_ != C_NONE) {
+              auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_];
               const DelayedGroupFilter& filt
                 {*dynamic_cast<DelayedGroupFilter*>(
                 model::tally_filters[i_dg_filt].get())};
@@ -836,8 +833,8 @@ score_general_ce(Particle* p, int i_tally, int start_index, int filter_index,
               const auto& rxn {*nuc.fission_rx_[0]};
               auto rate = rxn.products_[g].decay_rate_;
               score += simulation::keff * bank.wgt * rate * flux;
-              if (tally.delayedgroup_filter_ > 0) {
-                auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_-1];
+              if (tally.delayedgroup_filter_ != C_NONE) {
+                auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_];
                 const DelayedGroupFilter& filt
                   {*dynamic_cast<DelayedGroupFilter*>(
                   model::tally_filters[i_dg_filt].get())};
@@ -858,8 +855,8 @@ score_general_ce(Particle* p, int i_tally, int start_index, int filter_index,
           const auto& nuc {*data::nuclides[i_nuclide]};
           if (!nuc.fissionable_) continue;
           const auto& rxn {*nuc.fission_rx_[0]};
-          if (tally.delayedgroup_filter_ > 0) {
-            auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_-1];
+          if (tally.delayedgroup_filter_ != C_NONE) {
+            auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_];
             const DelayedGroupFilter& filt
               {*dynamic_cast<DelayedGroupFilter*>(
               model::tally_filters[i_dg_filt].get())};
@@ -890,8 +887,8 @@ score_general_ce(Particle* p, int i_tally, int start_index, int filter_index,
             }
           }
         } else {
-          if (tally.delayedgroup_filter_ > 0) {
-            auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_-1];
+          if (tally.delayedgroup_filter_ != C_NONE) {
+            auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_];
             const DelayedGroupFilter& filt
               {*dynamic_cast<DelayedGroupFilter*>(
               model::tally_filters[i_dg_filt].get())};
@@ -1238,8 +1235,7 @@ void
 score_general_mg(Particle* p, int i_tally, int start_index, int filter_index,
   int i_nuclide, double atom_density, double flux)
 {
-  //TODO: off-by-one
-  const Tally& tally {*model::tallies[i_tally-1]};
+  const Tally& tally {*model::tallies[i_tally]};
   auto results = tally_results(i_tally);
 
   //TODO: off-by-one throughout on p->material
@@ -1503,7 +1499,7 @@ score_general_mg(Particle* p, int i_tally, int start_index, int filter_index,
     case SCORE_NU_FISSION:
       if (tally.estimator_ == ESTIMATOR_ANALOG) {
         if (settings::survival_biasing || p->fission) {
-          if (tally.energyout_filter_ > 0) {
+          if (tally.energyout_filter_ != C_NONE) {
             // Fission has multiple outgoing neutrons so this helper function
             // is used to handle scoring the multiple filter bins.
             score_fission_eout(p, i_tally, score_index, score_bin);
@@ -1553,7 +1549,7 @@ score_general_mg(Particle* p, int i_tally, int start_index, int filter_index,
     case SCORE_PROMPT_NU_FISSION:
       if (tally.estimator_ == ESTIMATOR_ANALOG) {
         if (settings::survival_biasing || p->fission) {
-          if (tally.energyout_filter_ > 0) {
+          if (tally.energyout_filter_ != C_NONE) {
             // Fission has multiple outgoing neutrons so this helper function
             // is used to handle scoring the multiple filter bins.
             score_fission_eout(p, i_tally, score_index, score_bin);
@@ -1607,7 +1603,7 @@ score_general_mg(Particle* p, int i_tally, int start_index, int filter_index,
     case SCORE_DELAYED_NU_FISSION:
       if (tally.estimator_ == ESTIMATOR_ANALOG) {
         if (settings::survival_biasing || p->fission) {
-          if (tally.energyout_filter_ > 0) {
+          if (tally.energyout_filter_ != C_NONE) {
             // Fission has multiple outgoing neutrons so this helper function
             // is used to handle scoring the multiple filter bins.
             score_fission_eout(p, i_tally, score_index, score_bin);
@@ -1619,8 +1615,8 @@ score_general_mg(Particle* p, int i_tally, int start_index, int filter_index,
           // calculate fraction of absorptions that would have resulted in
           // delayed-nu-fission
           if (get_macro_xs(p->material, MG_GET_XS_ABSORPTION, p_g) > 0) {
-            if (tally.delayedgroup_filter_ > 0) {
-              auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_-1];
+            if (tally.delayedgroup_filter_ != C_NONE) {
+              auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_];
               const DelayedGroupFilter& filt
                 {*dynamic_cast<DelayedGroupFilter*>(
                 model::tally_filters[i_dg_filt].get())};
@@ -1669,8 +1665,8 @@ score_general_mg(Particle* p, int i_tally, int start_index, int filter_index,
           // score. Loop over the neutrons produced from fission and check which
           // ones are delayed. If a delayed neutron is encountered, add its
           // contribution to the fission bank to the score.
-          if (tally.delayedgroup_filter_ > 0) {
-            auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_-1];
+          if (tally.delayedgroup_filter_ != C_NONE) {
+            auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_];
             const DelayedGroupFilter& filt
               {*dynamic_cast<DelayedGroupFilter*>(
               model::tally_filters[i_dg_filt].get())};
@@ -1701,8 +1697,8 @@ score_general_mg(Particle* p, int i_tally, int start_index, int filter_index,
           }
         }
       } else {
-        if (tally.delayedgroup_filter_ > 0) {
-          auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_-1];
+        if (tally.delayedgroup_filter_ != C_NONE) {
+          auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_];
           const DelayedGroupFilter& filt
             {*dynamic_cast<DelayedGroupFilter*>(
             model::tally_filters[i_dg_filt].get())};
@@ -1741,8 +1737,8 @@ score_general_mg(Particle* p, int i_tally, int start_index, int filter_index,
           // calculate fraction of absorptions that would have resulted in
           // delayed-nu-fission
           if (get_macro_xs(p->material, MG_GET_XS_ABSORPTION, p_g) > 0) {
-            if (tally.delayedgroup_filter_ > 0) {
-              auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_-1];
+            if (tally.delayedgroup_filter_ != C_NONE) {
+              auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_];
               const DelayedGroupFilter& filt
                 {*dynamic_cast<DelayedGroupFilter*>(
                 model::tally_filters[i_dg_filt].get())};
@@ -1821,8 +1817,8 @@ score_general_mg(Particle* p, int i_tally, int start_index, int filter_index,
                   * get_macro_xs(p->material, MG_GET_XS_DECAY_RATE, p_g,
                                  nullptr, nullptr, &g);
               }
-              if (tally.delayedgroup_filter_ > 0) {
-                auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_-1];
+              if (tally.delayedgroup_filter_ != C_NONE) {
+                auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_];
                 const DelayedGroupFilter& filt
                   {*dynamic_cast<DelayedGroupFilter*>(
                   model::tally_filters[i_dg_filt].get())};
@@ -1837,11 +1833,11 @@ score_general_mg(Particle* p, int i_tally, int start_index, int filter_index,
               }
             }
           }
-          if (tally.delayedgroup_filter_ > 0) continue;
+          if (tally.delayedgroup_filter_ != C_NONE) continue;
         }
       } else {
-        if (tally.delayedgroup_filter_ > 0) {
-          auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_-1];
+        if (tally.delayedgroup_filter_ != C_NONE) {
+          auto i_dg_filt = tally.filters()[tally.delayedgroup_filter_];
           const DelayedGroupFilter& filt
             {*dynamic_cast<DelayedGroupFilter*>(
             model::tally_filters[i_dg_filt].get())};
@@ -1943,8 +1939,7 @@ score_general_mg(Particle* p, int i_tally, int start_index, int filter_index,
 void
 score_all_nuclides(Particle* p, int i_tally, double flux, int filter_index)
 {
-  //TODO: off-by-one
-  const Tally& tally {*model::tallies[i_tally-1]};
+  const Tally& tally {*model::tallies[i_tally]};
   const Material& material {*model::materials[p->material-1]};
 
   // Score all individual nuclide reaction rates.
@@ -1984,8 +1979,7 @@ extern "C" void
 score_analog_tally_ce(Particle* p)
 {
   for (auto i_tally : model::active_analog_tallies) {
-    //TODO: off-by-one
-    const Tally& tally {*model::tallies[i_tally-1]};
+    const Tally& tally {*model::tallies[i_tally]};
 
     // Initialize an iterator over valid filter bin combinations.  If there are
     // no valid combinations, use a continue statement to ensure we skip the
@@ -2049,8 +2043,7 @@ extern "C" void
 score_analog_tally_mg(Particle* p)
 {
   for (auto i_tally : model::active_analog_tallies) {
-    //TODO: off-by-one
-    const Tally& tally {*model::tallies[i_tally-1]};
+    const Tally& tally {*model::tallies[i_tally]};
 
     // Initialize an iterator over valid filter bin combinations.  If there are
     // no valid combinations, use a continue statement to ensure we skip the
@@ -2109,8 +2102,7 @@ score_tracklength_tally(Particle* p, double distance)
   double flux = p->wgt * distance;
 
   for (auto i_tally : model::active_tracklength_tallies) {
-    //TODO: off-by-one
-    const Tally& tally {*model::tallies[i_tally-1]};
+    const Tally& tally {*model::tallies[i_tally]};
 
     // Initialize an iterator over valid filter bin combinations.  If there are
     // no valid combinations, use a continue statement to ensure we skip the
@@ -2191,8 +2183,7 @@ score_collision_tally(Particle* p)
   }
 
   for (auto i_tally : model::active_collision_tallies) {
-    //TODO: off-by-one
-    const Tally& tally {*model::tallies[i_tally-1]};
+    const Tally& tally {*model::tallies[i_tally]};
 
     // Initialize an iterator over valid filter bin combinations.  If there are
     // no valid combinations, use a continue statement to ensure we skip the
@@ -2258,8 +2249,7 @@ score_surface_tally_inner(Particle* p, const std::vector<int>& tallies)
   double flux = p->wgt;
 
   for (auto i_tally : tallies) {
-    //TODO: off-by-one
-    const Tally& tally {*model::tallies[i_tally-1]};
+    const Tally& tally {*model::tallies[i_tally]};
     auto results = tally_results(i_tally);
 
     // Initialize an iterator over valid filter bin combinations.  If there are
diff --git a/src/tallies/trigger.cpp b/src/tallies/trigger.cpp
index ac69545c6..25bb0c8c0 100644
--- a/src/tallies/trigger.cpp
+++ b/src/tallies/trigger.cpp
@@ -30,7 +30,8 @@ static std::pair<double, double>
 get_tally_uncertainty(int i_tally, int score_index, int filter_index)
 {
   int n;
-  int err = openmc_tally_get_n_realizations(i_tally, &n);
+  //TODO: off-by-one
+  int err = openmc_tally_get_n_realizations(i_tally+1, &n);
 
   auto results = tally_results(i_tally);
   auto sum = results(filter_index, score_index, RESULT_SUM);
@@ -54,13 +55,13 @@ void
 check_tally_triggers(double& ratio, int& tally_id, int& score)
 {
   ratio = 0.;
-  //TODO: off-by-one
-  for (auto i_tally = 1; i_tally < model::tallies.size()+1; ++i_tally) {
-    const Tally& t {*model::tallies[i_tally-1]};
+  for (auto i_tally = 0; i_tally < model::tallies.size(); ++i_tally) {
+    const Tally& t {*model::tallies[i_tally]};
 
     // Ignore tallies with less than two realizations.
     int n_reals;
-    int err = openmc_tally_get_n_realizations(i_tally, &n_reals);
+    //TODO: off-by-one
+    int err = openmc_tally_get_n_realizations(i_tally+1, &n_reals);
     if (n_reals < 2) continue;
 
     for (const auto& trigger : t.triggers_) {