What is a standard descent gradient?

The 3:1 rule equates to a 3-degree descent angle and roughly 300 ft/min per 100 kts of groundspeed. Airlines typically plan 1,000-1,500 fpm for en-route descent, steepening to 700-800 fpm on the approach.

How early should I start descending?

Multiply the altitude to lose (in thousands of feet) by 3 to get the TOD distance in NM, then add 10% as a buffer for ATC routing or crossing restrictions. This calculator does that automatically in Normal mode.

How do you calculate top of climb (TOC)?

Divide the altitude to gain by your average climb rate to get the climb time in minutes, then multiply by ground speed to get the distance: TOC distance = (altitude to gain / climb rate) x (ground speed / 60). Climbing from 5,000 ft to FL350 at 1,800 fpm and 300 kts ground speed puts TOC about 83 NM out.

How do you calculate the required rate of descent?

Divide the altitude to lose by the time available: time (min) = distance (NM) / ground speed (kts) x 60, then required V/S = altitude to lose / time. The Descent Rate mode does this for a fixed distance to go - useful when ATC clears you to cross a fix at a given altitude.

Descent Planner

Top of Descent Calculator

Calculate your top of descent, top of climb, and the descent rate required to make a crossing restriction. Enter altitude, ground speed, and distance for instant results.

CalculatorInteractive

Calculation

Descent profile

3:1 rule + 10% buffer

Cruise Altitude

Target Altitude

Ground Speed

kts

Top of Descent

Start Descent106NM out

Descent Time14min

V/S Required-2273fpm

Alt to Lose32.0kft

ILS Glideslope (3 deg)

G/S V/S-2388fpm

At GS450kts

How to Use & Reference

About

Top of descent (TOD) is the point along your route where you begin descending from cruise altitude; top of climb (TOC) is where you level off after departure. Descending too early wastes fuel and speed; starting too late means you arrive above your target altitude and have to request an expedited descent from ATC. The standard 3:1 rule gives a quick estimate for a 3-degree descent profile, and the Descent Rate mode answers the everyday crossing-restriction question: what V/S do I need to make this fix?

How to Use

1Pick a calculation: Top of Descent, Top of Climb, or Descent Rate.
2TOD: select Normal (3:1 rule + 10% buffer) or Expedite (2:1 rule, no buffer), then enter cruise altitude, target altitude, and ground speed.
3TOC: enter your initial altitude, cruise altitude, average climb rate, and ground speed to see how far out you will reach cruise.
4Descent Rate: enter cruise and target altitude, the distance to go, and ground speed to get the V/S required to make the restriction.
5Read the distance, time, required V/S, and ILS glideslope V/S from the results.

Tips

The 3:1 rule gives 3 NM per 1,000 ft to lose. Descending from FL350 to 3,000 ft = 96 NM TOD.
Add the 10% buffer in Normal mode for realistic ATC routing - direct routing in the sim does not exist at busy airports.
Required V/S = altitude to lose / descent time in minutes. Cross-check against your aircraft's max continuous descent V/S.
For TOC, use the average climb rate over the whole climb - jets that climb at 2,500+ fpm low down often manage only 1,000-1,500 fpm approaching cruise.
At 300 kts groundspeed, a 3-degree ILS glideslope requires roughly 1,500 fpm. Dial this in before the final approach fix.
Plan for a 250 kt speed restriction at FL100 and below. Factor in the deceleration distance on top of the descent distance.

TOD / TOC Formulas

TOD (NM)(alt to lose / 1000) x ratio

Normal ratio3 x 1.1 (10% buffer)

Expedite ratio2 (no buffer)

TOC (NM)(alt to gain / climb rate) x (GS / 60)

V/S (fpm)alt to lose / time (min)

Required V/Salt to lose / (dist / GS x 60)

ILS V/SGS (kts) x 101.27 x tan(3deg)

ILS formula assumes a standard 3-degree glideslope.

FAQ

What is a standard descent gradient?: The 3:1 rule equates to a 3-degree descent angle and roughly 300 ft/min per 100 kts of groundspeed. Airlines typically plan 1,000-1,500 fpm for en-route descent, steepening to 700-800 fpm on the approach.
How early should I start descending?: Multiply the altitude to lose (in thousands of feet) by 3 to get the TOD distance in NM, then add 10% as a buffer for ATC routing or crossing restrictions. This calculator does that automatically in Normal mode.
How do you calculate top of climb (TOC)?: Divide the altitude to gain by your average climb rate to get the climb time in minutes, then multiply by ground speed to get the distance: TOC distance = (altitude to gain / climb rate) x (ground speed / 60). Climbing from 5,000 ft to FL350 at 1,800 fpm and 300 kts ground speed puts TOC about 83 NM out.
How do you calculate the required rate of descent?: Divide the altitude to lose by the time available: time (min) = distance (NM) / ground speed (kts) x 60, then required V/S = altitude to lose / time. The Descent Rate mode does this for a fixed distance to go - useful when ATC clears you to cross a fix at a given altitude.

How to Calculate Top of Climb

Top of climb (TOC) is where you level off at cruise altitude. Divide the altitude to gain by your average climb rate to get the climb time, then multiply that time by your ground speed: TOC distance (NM) = altitude to gain / climb rate x ground speed / 60. A climb from 5,000 ft to FL350 at 1,800 fpm and 300 kts takes about 17 minutes and levels off about 83 NM from where the climb began. Pick Top of Climb in the calculator above to run your own numbers.

Top of Climb Distance for a 30,000 ft Climb

Avg climb rate	Time	250 kts GS	300 kts GS	350 kts GS
1,500 fpm	20 min	83 NM	100 NM	117 NM
2,000 fpm	15 min	62 NM	75 NM	88 NM
2,500 fpm	12 min	50 NM	60 NM	70 NM

Uses the average climb rate and ground speed over the whole climb. Jets climb fastest low down and slowest approaching cruise, so plan with the average, not the initial rate.