diff --git a/Marlin/planner.cpp b/Marlin/planner.cpp
index c222da669..adbf14250 100644
--- a/Marlin/planner.cpp
+++ b/Marlin/planner.cpp
@@ -218,7 +218,7 @@ void Planner::calculate_trapezoid_for_block(block_t* const block, const float &e
 
           // Steps required for acceleration, deceleration to/from nominal rate
   int32_t accelerate_steps = CEIL(estimate_acceleration_distance(initial_rate, block->nominal_rate, accel)),
-          decelerate_steps = CEIL(estimate_acceleration_distance(block->nominal_rate, final_rate, -accel)),
+          decelerate_steps = FLOOR(estimate_acceleration_distance(block->nominal_rate, final_rate, -accel)),
           // Steps between acceleration and deceleration, if any
           plateau_steps = block->step_event_count - accelerate_steps - decelerate_steps;
 
diff --git a/Marlin/stepper.cpp b/Marlin/stepper.cpp
index 438fca62e..664022b64 100644
--- a/Marlin/stepper.cpp
+++ b/Marlin/stepper.cpp
@@ -733,11 +733,8 @@ void Stepper::isr() {
 
     #endif // LIN_ADVANCE
   }
-  else if (step_events_completed >= (uint32_t)current_block->decelerate_after && current_block->step_event_count != (uint32_t)current_block->decelerate_after) {
+  else if (step_events_completed > (uint32_t)current_block->decelerate_after) {
     uint16_t step_rate;
-    // If we are entering the deceleration phase for the first time, we have to see how long we have been decelerating up to now. Equals last acceleration time interval.
-    if (!deceleration_time)
-      deceleration_time = calc_timer_interval(acc_step_rate);
     MultiU24X32toH16(step_rate, deceleration_time, current_block->acceleration_rate);
 
     if (step_rate < acc_step_rate) { // Still decelerating?