Marathon / Race Time Predictor
Project marathon time from a recent 5k/10k/half (Riegel formula).
- Calculators
- Free to use
- Runs in your browser
Your input
Set your options
Run Marathon / Race Time Predictor
Private by default. Runs entirely in your browser — files never uploaded.
Three steps
How to use Marathon / Race Time Predictor
- Step 01
Pick your input
Paste your text into the box above.
- Step 02
Configure & run
Adjust the options (known distance km, known time minutes, target distance km, riegel exponent) and click Run. Everything happens in your browser via WebAssembly.
- Step 03
Download the result
A JSON document is downloadable below.
This tool runs entirely in your browser. Your file is never uploaded to our servers.
About marathon / race time predictor
Project marathon time from a recent 5k/10k/half (Riegel formula). It sits in the calculators shelf alongside 140 other calculators tools, needs no account, and keeps the same behaviour whether you open it here or call it through the REST API.
It works from what you type in rather than a file and gives back JSON. The work happens in your browser, so nothing is sent to us at all and the tool keeps working offline. The same operation is available programmatically at POST /v1/calc/marathon-time-predictor.
Marathon / Race Time Predictor questions
Does Marathon / Race Time Predictor upload my file?
No. Marathon / Race Time Predictor runs as WebAssembly inside this browser tab: the file is read from your disk by the page, processed on your own machine, and handed straight back. It is never sent anywhere, so there is nothing for us to store or delete.
Do I need an account to use Marathon / Race Time Predictor?
No. Marathon / Race Time Predictor works without signing in, and that is not a trial — it is how the free tier works. An account only matters for things that need one to exist at all: larger server jobs against your quota, API keys, saved workflows and billing.
Can I run Marathon / Race Time Predictor from my own code?
Yes. Every tool on the site is reachable from the REST API with the same slug — `marathon-time-predictor` — and the same options as this page, so anything you can do here you can automate against your own files.