Quick guide
How to use this calculator
- Choose the real journey or motion relationship first, then enter only the measurements that belong to that mode.
- Keep every distance, speed, duration, clock, direction, break, reserve, wind, or current convention explicit; the calculator normalizes compatible units internally.
- Use the companion outputs to reconcile the scenario, then retain the stated limits before using an estimate for a real journey.
Calculation method
How the relative speed, meeting and catch-up calculator works
Model relative motion explicitly instead of subtracting or adding speeds without accounting for the starting gap and start times.
At A’s start, same-direction separation adds B’s head-start distance and closing speed is A−B; opposite-direction separation subtracts B’s head-start distance and closing speed is A+B.
Worked example
Relative Speed, Meeting and Catch-Up example
With B 30 km ahead at 60 km/h and A following at 90 km/h without delay, A catches B after 1 hour and 90 km of A travel.
At A’s start, same-direction separation adds B’s head-start distance and closing speed is A−B; opposite-direction separation subtracts B’s head-start distance and closing speed is A+B.
Supported inputs
Precision and limits
Scenario boundary
This is an ideal constant-speed, one-dimensional model. It is not overtaking guidance and does not account for roads, collision avoidance, right-of-way, reaction time, traffic, acceleration, or safe separation.
Precision and time
Calculations retain working precision and round durations to the nearest second and clock outputs to the nearest minute. Entered averages and schedules remain assumptions, not live observations or guarantees.
Category ownership
This calculator handles neutral travel, timing, range, or relative-motion arithmetic. Vehicle operating cost and performance belong in Automotive; competition pacing belongs in Sports; time zones belong in Dates & Times; route geography belongs in Travel & Geography; advanced dynamics belong in Engineering & Science.
Privacy
Entered locations are not requested. Entered values and results stay in this browser and are not sent to analytics or third parties.
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