Advanced Race Time Predictor Calculator

Calculator Inputs

Distance Unit

Source Race Preset

Source Distance

Source Time (HH:MM:SS)

Target Race Preset

Target Distance

Fatigue Exponent

Typical running default: 1.06

Fitness Gain (%)

Positive values make the predicted time faster.

Course Penalty (%)

Use positive values for hills or harder terrain.

Weather Penalty (%)

Use positive values for heat, wind, or humidity.

Strategy Buffer (%)

Add margin for conservative pacing plans.

Split Interval

Example Data Table

Source Result	Target Race	Exponent	Adjustment	Predicted Time
5 km in 00:25:00	10 km	1.06	0%	00:52:08
10 km in 00:50:00	Half Marathon	1.06	0%	01:50:18
Half Marathon in 01:48:00	Marathon	1.06	0%	03:45:11

Formula Used

The calculator uses the well-known Riegel prediction model to estimate a new race time from a prior result.

Base prediction: T2 = T1 × (D2 ÷ D1)^k

Adjusted prediction: Base Time × (1 + Course %) × (1 + Weather %) × (1 - Fitness %) × (1 + Strategy %)

Pace: Predicted Time ÷ Target Distance

Speed: Target Distance ÷ Total Hours

Here, T1 is the known performance time, D1 is the known distance, D2 is the target distance, and k is the fatigue exponent.

How to Use This Calculator

Select the distance unit you want to use.
Choose a source race preset or enter a custom source distance.
Enter your recent race time in hours, minutes, and seconds.
Choose a target race preset or enter a custom target distance.
Set the fatigue exponent. Most runners can start with 1.06.
Add optional fitness, course, weather, and strategy adjustments.
Enter the split interval you want for the pacing table.
Press Predict Race Time to see results, graph, tables, and export options.

FAQs

1) What does this calculator predict?

It estimates a target race finish time from a known recent performance. It also shows paces, split intervals, adjustment impact, and equivalent standard race times.

2) Which sports is this best for?

It is mainly designed for running and road-race pacing. It can also help with similar endurance events when performance scales sensibly with distance.

3) What is the fatigue exponent?

The fatigue exponent controls how quickly performance slows as distance increases. Lower values suit stronger endurance profiles, while higher values reflect greater fade over longer races.

4) Why do adjusted results differ from base results?

Base prediction uses only distance scaling. Adjusted prediction also includes fitness gain, course difficulty, weather effects, and any extra pacing buffer you want to apply.

5) Should I use my latest race as the source result?

Yes, that usually gives the best estimate. Choose a recent performance completed with strong effort and similar conditions for more believable race projections.

6) Can this predict marathon times from short races?

Yes, but accuracy falls as the gap grows between source and target distances. Longer source races usually produce more reliable marathon predictions.

7) What split interval should I enter?

Use 1 kilometer or 1 mile for detailed pacing, or larger intervals such as 5 kilometers for cleaner long-race summaries and easier race-day planning.

8) Are these predictions guaranteed race outcomes?

No. They are planning estimates based on your inputs. Training status, fueling, pacing discipline, terrain, heat, and race-day execution can still change the final outcome.