diff --git a/service_capacity_modeling/capacity_planner.py b/service_capacity_modeling/capacity_planner.py
index 86c5655..54fa4c9 100644
--- a/service_capacity_modeling/capacity_planner.py
+++ b/service_capacity_modeling/capacity_planner.py
@@ -2,7 +2,7 @@
 import functools
 import logging
 from hashlib import blake2b
-from typing import Any
+from typing import Any, cast
 from typing import Callable
 from typing import Dict
 from typing import Generator
@@ -382,9 +382,10 @@ def _plan_percentiles(
                 )
             )
 
-        mean_plan = [
-            functools.reduce(merge_plan, composed) for composed in zip(*mean_plans)
-        ]
+        mean_plan = cast(
+            Sequence[CapacityPlan],
+            [functools.reduce(merge_plan, composed) for composed in zip(*mean_plans)],
+        )
         percentile_plans = {}
         for index, percentile in enumerate(sorted_percentiles):
             percentile_plan = []
@@ -404,10 +405,13 @@ def _plan_percentiles(
                         drives=drives,
                     )
                 )
-            percentile_plans[percentile] = [
-                functools.reduce(merge_plan, composed)
-                for composed in zip(*percentile_plan)
-            ]
+            percentile_plans[percentile] = cast(
+                Sequence[CapacityPlan],
+                [
+                    functools.reduce(merge_plan, composed)
+                    for composed in zip(*percentile_plan)
+                ],
+            )
 
         return mean_plan, percentile_plans
 
diff --git a/service_capacity_modeling/models/org/netflix/ddb.py b/service_capacity_modeling/models/org/netflix/ddb.py
index 3dd77dc..2a18a49 100644
--- a/service_capacity_modeling/models/org/netflix/ddb.py
+++ b/service_capacity_modeling/models/org/netflix/ddb.py
@@ -473,12 +473,15 @@ def capacity_plan(
             annual_balance_target = target_max_annual_cost - total_annual_costs
             if annual_balance_target > 0:
                 max_read_capacity_units += round(
-                    (annual_balance_target / max(1, read_plan.total_annual_read_cost))
+                    (annual_balance_target / max(1.0, read_plan.total_annual_read_cost))
                     * read_plan.read_capacity_units,
                     2,
                 )
                 max_write_capacity_units += round(
-                    (annual_balance_target / max(1, write_plan.total_annual_write_cost))
+                    (
+                        annual_balance_target
+                        / max(1.0, write_plan.total_annual_write_cost)
+                    )
                     * total_write_capacity_units,
                     2,
                 )
diff --git a/tests/netflix/test_ddb.py b/tests/netflix/test_ddb.py
index d222a24..a3ed25b 100644
--- a/tests/netflix/test_ddb.py
+++ b/tests/netflix/test_ddb.py
@@ -86,7 +86,7 @@
 
 
 def test_plan_storage():
-    result = planner.plan_certain(
+    result = planner.plan(
         model_name="org.netflix.dynamodb",
         region="us-east-1",
         num_regions=1,
diff --git a/tests/test_hardware.py b/tests/test_hardware.py
index 129726d..4da63a5 100644
--- a/tests/test_hardware.py
+++ b/tests/test_hardware.py
@@ -3,6 +3,6 @@
 
 def test_blob():
     s3 = shapes.region("us-east-1").services["blob.standard"]
-    assert s3.annual_cost_per_gib > 0
+    assert s3.annual_cost_gib(1) > 0
     assert s3.annual_cost_per_write_io > 0
     assert s3.annual_cost_per_read_io > 0