Pete Riegel Race Time Predictor Calculator

ByDr. Liam Gallagher, DPT, CSCS ✓ Verified 📚 248 Calculators Authored

Doctor of Physical Therapy & Sports Performance Scientist · Doctor of Physical Therapy (DPT), Certified Strength and Conditioning Specialist (CSCS)

📅 Published: Sep 28, 2026

The formula

T₂ = T₁ · (D₂ / D₁)^1.06 | Pace = Time / Distance

Origins and Clinical Validity of Pete Riegel’s Endurance Formula

Published in Runner’s World in 1977 by research engineer Pete Riegel, this formula models the aerobic decay curve of human runners across distances from 1,500 meters to 100 miles. The constant 1.06 reflects the empirical 6% loss in average velocity every time race distance doubles.

Frequently asked questions

Why might my actual marathon be slower than the Riegel prediction?

The Riegel formula assumes equivalent aerobic conditioning. If a runner trains only 20 miles per week for a 5K, they lack the mitochondrial density and glycogen storage required to sustain Riegel’s projected marathon pace without hitting "the wall" at mile 20.

Source & methodology

Riegel PS. "Athletic Records and Human Endurance." American Scientist. 1981.

Pete Riegel Race Time Predictor: what this tool answers

You are counting something that matters — this tool counts it exactly, including the edge cases calendars hide. Searchers land on a Pete Riegel Race Time Predictor page for three reasons — to plan, to compare options, and to check that somebody else’s arithmetic is honest. This tool serves all three, and everything after the calculator explains the model instead of hiding it.

Individual variation is large here: limb proportions, fibre mix and history all shift how a population-average Pete Riegel Race Time Predictor maps to you. Use it as a starting prescription, then let performance feedback over weeks tune it.

The useful way to hold Pete Riegel Race Time Predictor is as a ratio with a story attached: T₂ = T₁ · (D₂ / D₁)^1.06 | Pace = Time / Distance says how the parts combine, and the 12947.985804503194 figure above is simply that sentence written in numbers. Everything that follows unpacks one clause of the sentence at a time.

Nothing below is stock text pasted around a number: the worked example computes projected marathon finish time = 12947.985804503194 from this tool’s own defaults. Work down the page and by the end you could re-derive the result in a spreadsheet from memory.

Inside the Pete Riegel Race Time Predictor calculation: formula and every input

Here is the complete model this tool runs — T₂ = T₁ · (D₂ / D₁)^1.06 | Pace = Time / Distance — with each input explained below. If a competitor’s page gives you a different answer from the same inputs, this is the text that settles which of you is right.

Baseline Reference Race Distance (example value 5 Kilometers (5.00 km)) is a choice rather than a quantity — pick the option that matches your situation, because the calculation path branches here. Keep every length field in the same unit; the formula assumes a consistency it cannot check for you.

Baseline finish time (Hours) (example value 0) is a numeric input whose unit is fixed by the label; a wrong unit is a wrong answer wearing a plausible disguise. Be precise about the boundary (exact date, start of month); time inputs decide the exponent in most formulas.

Baseline finish time (Minutes) (example value 22) is a plain measured quantity — the unit shown in the label is the unit the formula expects. Be precise about the boundary (exact date, start of month); time inputs decide the exponent in most formulas.

Baseline finish time (Seconds) (example value 30) is a plain measured quantity — the unit shown in the label is the unit the formula expects. If the period is partial, decide whether you mean elapsed or planned time and keep that meaning across every field.

Pete Riegel Race Time Predictor on the example inputs: the complete substitution

The tool prints its own working; this is the same arithmetic on the example values, reproduced so you can follow it by hand. Starting figures: Baseline Reference Race Distance, Baseline finish time (Hours), Baseline finish time (Minutes), Baseline finish time (Seconds). The endpoint of that chain is 12947.985804503194 of projected marathon finish time, sitting in the “🟢 Predicted Marathon: 3:35:48 (05:07 /km) based on your 22:30 baseline.” band.

Baseline Race Time = 22:30 across 5.00 km
Riegel Aerobic Scaling Formula: T₂ = T₁ × (D₂ ÷ D₁)^1.06
Marathon Scaling = 22:30 × (42.195 ÷ 5.00)^1.06 = 3:35:48
Target Marathon Pace = 3:35:48 ÷ 42.195 km = 05:07 /km

Projected Marathon Time — 3:35:48. Compare it against the main result of 12947.985804503194 before drawing conclusions.

Projected Half Marathon Time — 1:43:30. This is the number experienced users quote when the headline alone would mislead.

Projected 10K Finish Time — 46:55. If your inputs change, this is usually the first companion figure to move.

Projected 5K Finish Time — 22:30. This is the number experienced users quote when the headline alone would mislead.

Riegel Fatigue Factor — 1.06. This is the number experienced users quote when the headline alone would mislead.

Overwrite any input above and every line of this example updates with it — the substitution is live, not a screenshot of somebody else’s numbers.

Interpreting the Pete Riegel Race Time Predictor verdict

Nobody acts on a bare figure — they act on a figure with a comparison attached. The verdict attached to the default calculation — “🟢 Predicted Marathon: 3:35:48 (05:07 /km) based on your 22:30 baseline.” — is one band on a ladder your own figure may sit somewhere else on. The practical reading rules: read the band as a starting hypothesis, then test it: change the two dominant inputs by ten percent and see whether the verdict survives. Verdicts that survive stress are the ones worth acting on.

In Fitness & Sports, Pete Riegel Race Time Predictor is one instrument in an orchestra: on its own it is a number, next to Projected Marathon Time and Projected Half Marathon Time it becomes a diagnosis. The tools linked above exist so the headline never has to carry that weight alone.

How people get Pete Riegel Race Time Predictor wrong

Chasing precision in Baseline finish time (Hours) while Baseline Reference Race Distance is still a guess. The sensitivity ranking above shows exactly where the accuracy budget should go.

The subtlest error is answering the wrong question precisely. Confirm that projected marathon finish time is actually the quantity your decision needs — the arithmetic is flawless either way, which is what makes the mistake invisible.

Pete Riegel Race Time Predictor verification checklist

Confirm the example values are plausible for your own situation before replacing them.
Compare the result with one independent method or published benchmark.
Confirm the inputs are dated — a Pete Riegel Race Time Predictor figure should carry the date it was computed.
Verify each input against its original source document, not memory.
Re-run the calculation with a ±10 % stress on the two most sensitive inputs.
Confirm the answer against one independent method or published benchmark for Pete Riegel Race Time Predictor.

Step by step: getting a trustworthy Pete Riegel Race Time Predictor out of this tool

Using a calculator well sounds trivial, but the difference between a decision-grade figure and a throwaway one lives entirely in the routine. The routine for Pete Riegel Race Time Predictor takes a minute to learn and applies to every input above.

Step 1 — one document, one pass. Open the statement, label or record that holds baseline reference race distance, baseline finish time (hours), baseline finish time (minutes), baseline finish time (seconds) and transcribe straight into the form. Transcription from a single source removes the mismatch errors that appear when figures are assembled from three different places. The test of a good estimate is not that it feels right but that it changes what you do.

Step 2 — start from the case you can defend. Enter pessimistic-but-honest figures first; the optimistic run is a ceiling, not a plan. A conclusion that holds on conservative inputs holds everywhere. Repeating a calculation with the same numbers proves only that the arithmetic is reliable — which is worth knowing.

Step 3 — play with the inputs on purpose. Ten percent up, ten percent down, one field at a time. Within a few minutes you will know this calculation better than most people who quote its results. A calculation you cannot explain to somebody else is a calculation you cannot defend.

Step 4 — ask what would have to be true. Take the result you want and work backwards through the inputs until you find the assumption that produces it; then decide honestly whether that assumption is defensible. If the answer changes your behaviour, it deserves a second run with different assumptions.

Step 5 — schedule the next run. In Fitness & Sports the inputs drift quietly. Put a reminder a quarter out, re-enter the same fields, and read the change rather than the level. Write the assumptions in the same file as the result, and future arguments take minutes instead of meetings.

Where Pete Riegel Race Time Predictor matters in practice

In Running the figure computed here is usually the first one somebody asks to see. Having it — with the formula behind it — changes your position in the conversation from participant to reference. A figure with a date beside it becomes evidence; without one it stays an anecdote.

Used properly this is a five-minute filter that saves weeks. Compute Pete Riegel Race Time Predictor, reject what fails, and only then bring in the expensive analysis for the survivors. The inputs are the part of the work that nobody else can do for you.

There is a personal-administration use people overlook: periodic self-checking. Pete Riegel Race Time Predictor quietly drifts as life changes — rates move, bodies change, costs compound — and re-running it a few times a year catches drift while correction is still cheap. The fastest sanity test is to guess the answer first and see how far the calculation disagrees.

Key terms on this page

Projected Marathon Time: 3:35:48 for the Pete Riegel Race Time Predictor worked case; it sits next to the main result because it carries context the headline leaves out.
Projected Half Marathon Time: 1:43:30 for the Pete Riegel Race Time Predictor worked case; it sits next to the main result because it carries context the headline leaves out.
Projected 10K Finish Time: 46:55 for the Pete Riegel Race Time Predictor worked case; it sits next to the main result because it carries context the headline leaves out.
Projected Marathon Finish Time: The primary output of this tool: 12947.985804503194 for the default inputs, computed exactly from T₂ = T₁ · (D₂ / D₁)^1.06 | Pace = Time / Distance.
Worked example: The step-by-step substitution printed above, so the arithmetic can be re-derived by hand or in a spreadsheet.
Verdict band: The plain-language label — here “🟢 Predicted Marathon: 3:35:48 (05:07 /km) based on your 22:30 baseline.” — mapping the computed figure onto experience-based ranges for Fitness & Sports.

Method, sources and what this tool cannot tell you

There is no black box on this page — the engine evaluates T₂ = T₁ · (D₂ / D₁)^1.06 | Pace = Time / Distance. Source of record: Riegel PS. "Athletic Records and Human Endurance." American Scientist. 1981. Specialist software layers extra coefficients on top of the same algebra; none are hidden here, and that transparency is what makes a disagreement traceable to a specific input instead of a black box.

Treat the output as a precise answer to the question you typed: exact arithmetic, transparent formula, published source, no hidden rounding. Every intermediate value is printed so that the result can be checked line by line rather than accepted or rejected wholesale.

After the number: what to do with it

Mark the computed date or span in your calendar with its assumptions attached; plans drift when the inputs do.

This page was written for people planning around a point or span in time, and the promise is that nothing above required trust. Bookmark the tool, re-run it whenever an input moves by more than a few percent, and keep the date with the number.