How the time is estimated
Airborne minutes = distance divided by ground speed, multiplied by 60. The allowance is then added as fixed minutes, because taxiing, the slower climb and the descent do not scale with cruise speed.
Ground speed, not indicated or true airspeed, is what moves the aircraft over the ground. A headwind lowers it and a tailwind raises it.
Worked example
A 3,450 mile route at an average ground speed of 500 mph takes 414 minutes in the air. Adding the 30 minute allowance gives 444 minutes, or 7 hours 24 minutes.
These figures are illustrative. Use the distance and ground speed from your own flight plan.
Why the allowance is separate
A short hop spends a much larger share of its time taxiing and climbing than a long-haul flight. Modelling that as a fixed allowance keeps the estimate honest for both, instead of applying a percentage that would overstate a short flight.
If you have a real taxi time from the airport, use it. Busy hubs can add 20 minutes on the ground before the wheels leave.
Limits of this calculator
It does not model winds aloft, step climbs, holding, slot delays or the difference between planned and actual routing. It is not a substitute for an operational flight plan.
For the distance itself, use the flight distance calculator.
To measure the great-circle distance first, use the US flight distance calculator.
Inputs for the US flight time calculator
Route distance
Planned or great-circle distance in statute miles, not kilometres.
Average ground speed
Cruise speed adjusted for wind. A headwind lowers the ground speed you enter.
Taxi, climb and approach allowance
Fixed minutes for the phases that do not scale with cruise speed. Thirty minutes is typical.
CALCULATOR QUESTIONS
US flight time calculator questions
Should I use airspeed or ground speed?
Ground speed. Airspeed ignores wind, and wind is what decides how long the leg actually takes.
Why is the allowance not a percentage?
Taxi and climb are roughly fixed, so a percentage would overstate short flights and understate long ones.
Does this include time-zone changes?
No. It gives elapsed time, not local arrival time.
Can I use it for a car journey?
It is arithmetic that works for any average speed, but the allowance is designed for aircraft phases.