diff --git a/app/pages/backtests.py b/app/pages/backtests.py
index ec804da..cb3e6bc 100644
--- a/app/pages/backtests.py
+++ b/app/pages/backtests.py
@@ -803,21 +803,13 @@ def _render_backtests_page(workspace_id: str | None = None) -> None:
                 mark_results_stale()
 
         def on_form_change() -> None:
+            """Handle form changes with minimal API calls."""
             validation_label.set_text("")
-            entry_spot, entry_error = derive_entry_spot()
+            # Only update cost estimate, don't derive entry spot on every change
+            # Entry spot derivation is expensive (Databento API call)
             update_cost_estimate()
-            render_seeded_summary(entry_spot=entry_spot, entry_spot_error=entry_error)
-            if entry_error:
-                entry_spot_hint.set_text("Entry spot unavailable until the scenario dates are valid.")
-                validation_label.set_text(entry_error)
-                render_result_state("Scenario validation failed", entry_error, tone="warning")
-                return
-            validation_error = validate_current_scenario(entry_spot=entry_spot)
-            if validation_error:
-                validation_label.set_text(validation_error)
-                render_result_state("Scenario validation failed", validation_error, tone="warning")
-            else:
-                mark_results_stale()
+            # Keep existing entry spot, don't re-derive
+            mark_results_stale()
 
         def run_backtest() -> None:
             validation_label.set_text("")
@@ -924,17 +916,19 @@ def _render_backtests_page(workspace_id: str | None = None) -> None:
             render_result(result)
 
         # Wire up event handlers
+        # Only call expensive derive_entry_spot on date changes
         data_source_select.on_value_change(lambda e: on_form_change())
-        dataset_select.on_value_change(lambda e: on_form_change())
+        dataset_select.on_value_change(lambda e: (update_date_range_hint(), on_form_change()))
         schema_select.on_value_change(lambda e: on_form_change())
-        symbol_select.on_value_change(lambda e: (update_date_range_hint(), on_form_change()))
+        symbol_select.on_value_change(lambda e: update_date_range_hint())
         start_input.on_value_change(lambda e: refresh_workspace_seeded_units())
         end_input.on_value_change(lambda e: refresh_workspace_seeded_units())
-        start_price_input.on_value_change(lambda e: on_form_change())
-        template_select.on_value_change(lambda e: on_form_change())
-        units_input.on_value_change(lambda e: on_form_change())
-        loan_input.on_value_change(lambda e: on_form_change())
-        ltv_input.on_value_change(lambda e: on_form_change())
+        # Don't trigger API calls on these changes
+        start_price_input.on_value_change(lambda e: mark_results_stale())
+        template_select.on_value_change(lambda e: mark_results_stale())
+        units_input.on_value_change(lambda e: mark_results_stale())
+        loan_input.on_value_change(lambda e: mark_results_stale())
+        ltv_input.on_value_change(lambda e: mark_results_stale())
         run_button.on_click(lambda: run_backtest())
 
         # Initial render