📍 Top of Descent
When to start descending from cruise altitude
About this calculator
The Top of Descent calculator finds where to begin descending for a planned arrival. Enter cruise altitude, target altitude, groundspeed, and desired descent rate or gradient; it computes the distance from the destination to start down, typically using the 3-to-1 rule — 3 nautical miles per 1,000 feet to lose.
Tip: start a few miles early when descending into a busy terminal area — ATC vectors and speed restrictions almost always stretch the descent, and being high and fast at the fix is the classic setup for an unstable approach.