Equal Time Point Calculator
The equal time point (ETP) is the critical navigation planning concept for overwater and remote area operations. It is the geographic point at which the time to continue to destination equals the time to return to the departure or alternate airport. Knowing the ETP helps pilots and dispatchers identify divert decision points along the route. The ETP location shifts with wind: a strong headwind on the outbound leg moves the ETP closer to the departure, giving more route to cover before the decision point. This calculator computes ETP distance and time from both ends, given total route distance and wind-corrected ground speeds in each direction.
Equal time point formula
ETP Distance from Departure = Total Distance x GS(return) / (GS(fwd) + GS(return))
Time to Destination from ETP = (Total Distance - ETP Distance) / GS(fwd)
Time to Return from ETP = ETP Distance / GS(return)
At the ETP, time to continue equals time to return: these two times will be equal (within rounding). The formula is from ICAO Doc 9976 (Flight Planning and Fuel Management Manual) and the FAA Aeronautical Information Manual. Ground speeds must be actual ground speeds (TAS with wind correction), not TAS alone.
ETOPS and oceanic applications
- For ETOPS flights, the ETP must be within the authorized diversion time (e.g., 180 minutes) of an adequate alternate airport.
- Oceanic tracks (North Atlantic, Pacific) require ETP calculations to filed alternates for dispatch.
- The ETP is recalculated for each divert-to airport along the route, not just the departure.
- Multiple ETPs can exist on a long route if multiple alternates are planned.
Equal time point calculator: frequently asked questions
What is the equal time point?
The equal time point (ETP), also called the point of equal time (PET) or critical point, is the geographic point on a route where it takes the same time to continue to destination as to return to the departure point. It is essential for oceanic and ETOPS routing where divert options are limited.
How is ETP calculated?
ETP Distance from Departure = Total Distance x (Ground Speed Return) / (GS Continue + GS Return). The ETP is expressed as a distance from the departure point. If GS to destination equals GS return, the ETP is at the midpoint. A headwind on the return makes the ETP closer to the destination.
What is the difference between ETP and PNR?
The ETP (equal time point) is where time to continue equals time to return. The PNR (point of no return) or PNF (point of no return on fuel) is where you have just enough fuel to return to the departure point. They are different concepts. The ETP is a time-based decision; the PNR is fuel-based.
Why does ETOPS planning use the ETP?
ETOPS (Extended Operations) requires that twin-engine aircraft always be within a specified diversion time (60, 120, 180 minutes) of an adequate airport. The ETP determines the worst-case divert time at any point on the route, ensuring the route is within the ETOPS authorization.
How does wind affect the ETP?
Wind shifts the ETP. A headwind on the outbound leg reduces ground speed to destination, shifting the ETP toward the departure. A tailwind on the return also shifts the ETP toward the departure (faster return reduces the time to return). Always calculate ETP with actual wind-corrected ground speeds.
Official sources
- ICAO Doc 9976 Flight Planning and Fuel Management Manual: icao.int.
- FAA Aeronautical Information Manual (AIM), Chapter 7: faa.gov.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.