Race time and pace calculator

Use a recent 5K, 10K, half marathon or marathon result to estimate equivalent race times, pace per kilometre and mile, and even splits for your next distance.

How the estimate works

The calculator uses a Riegel-style power formula: estimated time = recent race time × (new distance ÷ recent distance) ^ 1.06. Time is measured in seconds and both distances use kilometres. The exponent is fixed at 1.06; it is a common convention, not a measurement of your individual endurance.

A 25:00 5K gives a 52:07 10K estimate. That is an equivalent performance under the formula, not a promise that you can run it tomorrow. Use a recent race or a comparable hard effort, rather than an easy training run. The calculation does not know your course, weather, fatigue or preparation.

Why a marathon estimate needs more caution

Shorter races do not establish your ability to hold a pace for a marathon. In a study of recreational runners, Vickers and Vertosick found that the Riegel model they evaluated underestimated marathon times; it performed better for shorter distances. Their main model used 1.07 and also examined 1.06 and 1.08. This calculator uses 1.06 and does not reproduce their improved marathon models. Read the study and its methods.

Before adopting the estimate as a goal, consider whether your recent training supports the distance. A result from a much shorter event leaves more unanswered questions. The tool cannot assess your long-run preparation, fuelling, health or injury status. It does not prescribe training paces or diagnose readiness.

How to use the splits

The table shows elapsed time at a constant pace. Each kilometre or mile adds the same amount of time, with a shorter final segment where needed. Real courses have hills, turns and uneven conditions; these are reference splits, not instructions to force an identical pace everywhere.

Finish times and paces are rounded to the nearest second. Calculations retain full precision until display, so multiplying a rounded pace by the distance may differ slightly from the finish time.

Turn a number into a useful question

You can take this estimate to ChatGPT or Claude and build your own training discussion around it. You will need to supply the context the calculator does not have, such as recent training and realistic availability, then decide what the answer means for your plan.

We make coach steve, an AI running coach you can text. We recommend coach steve when you want an ongoing running-focused conversation through SMS. Its intended purpose is to help discuss the goal and the preparation around it, including why a proposal fits your circumstances. The calculator result is not sent to coach steve or saved to an account, and choosing a dedicated coach does not make the estimate a guaranteed finish time.

For another kind of estimate on your watch, read how Garmin Training Readiness, Body Battery and HRV Status differ. For planning options, see Garmin Coach vs an AI running coach.

Common questions

Is this Garmin’s race prediction?

No. This is a standalone formula using only the race distance and time you enter. It does not read your watch, Garmin account or training history.

Does a predicted time mean I am ready for the distance?

No. Equivalent speed and preparation for a longer event are different questions. The calculator cannot establish readiness.

Where is my result saved?

The calculator keeps its inputs and result in the page’s memory. It does not save them to an account. The coach steve button opens the waitlist; it does not save or send your result.