Race Time Predictor

Estimate your finish time at any distance — from 1K to marathon and beyond — based on a recent race result. This calculator uses Riegel's formula, the standard model used by running federations worldwide. Once you have a predicted goal time, use our race pace calculator to plan your splits.

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How to predict your race time

How the race time predictor works and frequently asked questions

What is a race time predictor?

A race time predictor estimates how fast you could finish a race at a different distance based on a recent result. It is most useful for setting a realistic goal time for an upcoming race based on your current fitness — not guessing.

Having a realistic baseline helps you determine training paces, fueling strategies, and race-day plans before you start a training block.

How the race time predictor works

This calculator uses Riegel's formula, developed by Peter Riegel:

T₂ = T₁ × (D₂ / D₁)^1.06

T₁ — your recent race time
D₁ — the distance you raced
D₂ — your target race distance
T₂ — the predicted finish time
1.06 — the fatigue factor, accounting for pace slowing as distance increases

The formula works well for standard race distances from 1K through to a full marathon. It is most accurate when the input and target distances are within a reasonable range of each other.

Example race time predictions

The table below shows predicted finish times at common race distances based on sample 5K starting times. All predictions use Riegel's formula with the standard 1.06 fatigue factor.

5K time	10K	Half marathon	Marathon
20:00	41:29	1:31:46	3:11:51
22:00	45:38	1:40:57	3:31:06
25:00	51:51	1:54:48	3:59:53
28:00	58:05	2:08:39	4:28:39
30:00	1:02:14	2:17:20	4:46:49
35:00	1:12:37	2:41:28	5:37:16

These predictions assume flat road conditions and a pacing strategy appropriate for the distance. Your actual race time will depend on training, weather, course profile, and race-day execution.

When to use a race time predictor

Setting a race goal

Before starting a training block for a half marathon or marathon, plug in a recent 5K or 10K result to get a realistic goal time. This prevents training for an unrealistic pace — or setting a target too easy.

Planning training paces

Once you have a predicted race time, work backwards to calculate training paces for tempo runs, intervals, and long runs. Many coaches use predicted race times as the anchor for an entire training programme.

Choosing a race distance

Not sure whether to sign up for a 10K or a half marathon? Predict your time for both based on a recent result to help decide where to focus your training.

Tracking fitness over time

Run the same race distance every few months and track how your predicted times at longer distances change. Improving predictions without racing the longer distance confirms your training is working.

Race time predictor vs pace calculator

A race time predictor answers: "How fast could I finish this distance?" based on a result at a different distance — for goal-setting before a training block.

A pace calculator answers: "What pace do I need to hit my target time?" and provides a split chart — for pacing strategy in the final weeks before a race.

Use the predictor first to set a goal, train for it, then use a pace calculator to map out race-day splits.

Tips for accurate race time predictions

Use a recent race time — ideally within the last 2–3 months.
Use an all-out effort — the prediction assumes a genuine race effort, not an easy training run.
Match the race type — road-to-road predictions are most reliable.
Keep distance ratios moderate — predicting a 10K from a 5K is highly accurate; predicting a marathon from a 1K is not.
Use multiple inputs — if you have recent results at two or more distances, run predictions for each to get a realistic window.

Frequently asked questions

This calculator uses Riegel's formula: T₂ = T₁ × (D₂/D₁)^1.06. T₁ is your recent race time, D₁ is the distance you raced, D₂ is your target distance, and T₂ is the predicted time. The 1.06 exponent is the fatigue factor that models how pace slows over longer distances.

Predictions are most accurate when you use a recent race time (within 2–3 months) and when the input and target distances are reasonably close. Predicting a 10K from a 5K is highly reliable. Predicting a marathon from a 1K is not, because endurance, fueling, and mental toughness become much larger factors over longer distances.

You can, but the prediction will be less accurate. The formula assumes your input time represents a genuine all-out race effort. A hard parkrun or time trial works well. An easy social run will produce an overly conservative estimate.

The formula predicts physiological potential based on your input time. It assumes you have done the distance-specific training — long runs, marathon-pace sessions, fueling practice. If you predict a marathon from a 5K time without that training, your actual time will likely be slower. The prediction is potential, not a guaranteed outcome.

A race time predictor estimates what you could run at a new distance. A pace calculator takes a known target time and breaks it into km or mile splits for race-day pacing. Use the predictor to set a goal, then a pace calculator for your race-day strategy.

Yes. Select "Custom" and enter any distance in kilometres or miles. This works for non-standard races like 15K, 25K, or ultra distances — though accuracy decreases when distances differ significantly.

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Race Time Predictor

Predicted results