Turn a training split into a race plan you can follow

This calculator has two modes. Predict mode estimates a full finish time based on your current pace and a simplified fatigue slowdown profile. Plan mode builds a split schedule for a target finish time. Splits are listed every 5 km, and you can switch between kilometers and miles for display.

Predict finish time Target pace plan Split table and charts Compare and PDF
Finish
Estimated race time
Pace
Average pace per unit
Splits
5 km schedule

How to use the Marathon Time Predictor

  1. 1

    Choose a mode

    Select Predict Finish Time to estimate your finish, or Target Pace Planner to build a plan for a goal finish time.

  2. 2

    Enter inputs

    In Predict mode, enter distance covered and elapsed time. In Plan mode, enter your target finish time.

  3. 3

    Select race distance

    Choose full marathon, half marathon, or custom distance. Switch units to show kilometers or miles.

  4. 4

    Calculate and export

    Press Calculate to see finish time, average pace, splits, charts, scenario compare, and export PDF.

Detailed guide and references▶

What this tool does

Marathon pacing is mostly about matching effort to a distance that is long enough to punish early mistakes. This page helps you in two ways: estimate a finish time from a partial run, or generate a clean split plan for a target finish time.

Runners in a marathon race
A split plan is easier to follow than guessing your pace on race day

Modes

Predict Finish Time

  • Enter a distance you already ran and the time it took.
  • Select a runner level to apply a simplified slowdown pattern.
  • The result is an estimated finish time and a forward-looking split schedule.

Target Pace Planner

  • Enter your desired finish time.
  • The tool computes a steady average pace and provides split times every 5 km.

Pace decay

Pace decay is a simplified way to model fatigue. This tool applies a fixed slowdown factor after a distance threshold that depends on runner level. It is not a physiological model. It is a practical estimate that can help you avoid overly optimistic pacing.

  • Beginner: higher decay and earlier decay start
  • Intermediate: moderate decay and later decay start
  • Elite: small decay and latest decay start

Splits and pacing

Splits are shown in 5 km steps to match common race signage and pacing habits. If you select miles, distances are shown in miles, but the step logic still follows 5 km internally.

  1. Use the average pace as your anchor, especially early.
  2. Expect some drift later, even with smart pacing.
  3. Practice the plan in long runs to validate it.

Limitations

This tool is for education and planning, not a guarantee.

  • It does not account for course elevation, heat, wind, or fueling.
  • GPS and manual input errors can skew predictions.
  • Fatigue varies widely by training and race conditions.

FAQs

What is pace decay in this tool?▶

Pace decay is a simplified slowdown model. The calculator gradually increases predicted pace after a distance threshold based on runner level.

Are splits every 5 km even if I select miles?▶

Yes. The split plan uses 5 km steps internally. When you select miles, the table displays the equivalent mile marks and pace per mile.

Can I use custom distances?▶

Yes. Choose Custom Distance and enter any distance in your chosen unit.

Does this account for hills and weather?▶

No. Consider this a starting point and adjust for course profile, conditions, and fueling strategy.

Key takeaways

  • Predict mode estimates finish time from a partial run with a simple fatigue slowdown profile
  • Plan mode builds a steady pacing schedule for a target finish time
  • Splits are listed every 5 km to simplify pacing decisions
  • Save scenarios to compare different inputs and goals
  • Use real course conditions and fueling to adjust the plan

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Calculator

Choose mode, enter inputs, then press Calculate

These results are for reference only and were developed for educational and testing purposes.