VDP Calculator - Calculator Academy

Enter the height above touchdown, descent rate, and runway threshold into the calculator to determine your vertical descent point (VDP).

VDP Formula

The visual descent point (VDP) is the point on a nonprecision approach where a normal visual descent to the touchdown zone can begin. This calculator uses height above touchdown, descent gradient, and runway threshold distance reference to compute the VDP in nautical miles or DME.

VDP = \frac{HAT}{DR} + RT

VDP = visual descent point distance
HAT = height above touchdown
DR = descent gradient in distance-based units such as ft/NM
RT = runway threshold distance reference

The calculation first determines how many nautical miles are needed to lose the required altitude at the selected descent gradient, then shifts that value by the runway threshold reference so the result matches the correct DME or distance reference used on the approach.

Rearranged Forms

If you are solving for a different variable, these equivalent forms are useful:

HAT = (VDP - RT)\times DR

DR = \frac{HAT}{VDP - RT}

RT = VDP - \frac{HAT}{DR}

Input Guide

Field	Meaning	Common Units	What to Enter
HAT	Height above touchdown zone elevation	ft, m, km	The vertical distance between the aircraft and the touchdown zone reference elevation
DR	Descent gradient	ft/NM, m/NM	A distance-based descent rate, not a time-based vertical speed
RT	Runway threshold reference	NM, km	The threshold position on the same distance reference used for the approach
VDP	Visual descent point	NM, km	The computed location where a normal descent may begin

How to Use the Calculator

Enter the height above touchdown, not field elevation and not altitude above mean sea level.
Enter the descent gradient in feet per nautical mile or meters per nautical mile.
Enter the runway threshold reference if the threshold is not located at zero on the distance scale you are using.
Provide any three values and let the calculator solve for the missing one.
Confirm that all distances use the same reference system before interpreting the result.

Example

If the height above touchdown is 600 ft, the descent gradient is 300 ft/NM, and the runway threshold reference is 0.3 NM, the VDP is:

VDP = \frac{600}{300} + 0.3

VDP = 2.3 \text{ NM}

In that case, the descent would begin at 2.3 on the same DME or distance reference used for the approach, assuming the runway environment is visible and the aircraft can continue on a normal, stabilized path.

What Affects the VDP

Higher HAT moves the VDP farther from the runway because more altitude must be lost.
Steeper descent gradients move the VDP closer in because altitude is lost over less distance.
Larger threshold offsets increase the reported VDP value by the same amount.
A commonly used planning approximation is that a 3° descent path is about 300 ft per nautical mile.

Common Mistakes

Using altitude MSL instead of height above touchdown.
Entering feet per minute instead of feet per nautical mile.
Ignoring a threshold offset on DME-based references.
Mixing kilometers and nautical miles without converting.
Assuming the computed value replaces the published approach procedure or stabilized approach criteria.

Special Case

If the runway threshold is the zero-distance reference, the threshold term drops out and the VDP depends only on height above touchdown and descent gradient:

VDP = \frac{HAT}{DR}

This makes the calculator especially useful for quick planning, training scenarios, and checking whether a selected descent profile produces a reasonable visual descent point before the threshold.