diff --git a/src/bedit_gui/controllers/simulation_run_controller.py b/src/bedit_gui/controllers/simulation_run_controller.py
index ddc949a..a0d85cf 100644
--- a/src/bedit_gui/controllers/simulation_run_controller.py
+++ b/src/bedit_gui/controllers/simulation_run_controller.py
@@ -47,8 +47,8 @@ class SimulationRunController(QObject):
     def start(self) -> None:
         if self._running or self.session is None:
             return
-        start_time = self.session.current_end_time
-        stop_time = start_time + self.session.settings.duration
+        start_time = self.session.settings.start_time
+        stop_time = self.session.current_end_time + self.session.settings.duration
         self._running = True
         self._update_actions()
         logger.info("Starting simulation from %s to %s", start_time, stop_time)
diff --git a/src/bedit_simulation/runtime.py b/src/bedit_simulation/runtime.py
index 0298b26..7633828 100644
--- a/src/bedit_simulation/runtime.py
+++ b/src/bedit_simulation/runtime.py
@@ -46,13 +46,15 @@ class SimulationSession:
         return self._simulation.is_running
 
     async def run_next(self) -> SimulationResult:
-        start_time = self.current_end_time
-        stop_time = start_time + self.settings.duration
-        intervals = math.ceil(self.settings.duration / self.settings.step_size) if self.settings.use_timed_steps else self.settings.number_of_steps
+        start_time = self.settings.start_time
+        stop_time = self.current_end_time + self.settings.duration
+        run_duration = stop_time - start_time
+        intervals = math.ceil(run_duration / self.settings.step_size) if self.settings.use_timed_steps else math.ceil(self.settings.number_of_steps * run_duration / self.settings.duration)
         options = SimulationOptions(start_time=start_time, stop_time=stop_time, number_of_intervals=intervals, tolerance=self.settings.tolerance, method=self.settings.method)
         result = await self._simulation.run(options)
+        # TODO: Continue from OpenModelica restart state instead of recomputing the full time range.
         self.current_end_time = stop_time
-        self.results.append(result)
+        self.results[:] = [result]
         return result
 
     def cancel(self) -> bool: