About RunDida

Free running tools built by a runner, for every runner.

The Runner Behind RunDida

I started running in 2020, at a low point. Work, life, relationships — everything felt stuck, and I was sleeping badly. Running was how I forced myself out of it.

The first run was 1 kilometer. Then 2, 3, 5, 8, 10. My pace crawled down from over 8 minutes per kilometer to 7, then 6. I ran 200 km that first year. Now I run more than 1,000 km a year.

In 2024 I ran my first marathon, the Shanghai Marathon, and finished in 4:08:31.

I'll be honest: that marathon started out as something to prove. I wanted evidence that I could take on something hard and actually finish it. But somewhere in all those kilometers, the proving stopped mattering. I had simply fallen in love with running, and it became part of how I live.

These days I don't chase mileage or pace anymore. I keep a rhythm that feels easy and sustainable, because the goal has changed: I want to still be running at 30, at 40, at 50, at 60 and beyond.

Why “RunDida”

RunDida is “run” + “dida” (滴答) — the Chinese onomatopoeia for the tick-tock of a clock's second hand. The site began as a personal countdown: how many days until my next marathon?

Then came the obvious next question — why not build this for every runner? So the countdown grew into a full toolbox: the training tools and race-day calculators that used to live only in coaching manuals and premium apps, free for everyone. That is the story of RunDida.

What We Offer

  • 100 Running Calculators — pace, splits, finish time, heart rate zones, VO2max, plus dedicated HYROX tools
  • Training Plans — 7 free plans with printable long and calendar views
  • Marathon Database — 300+ races worldwide with course details, weather history, registration windows, countdowns, and city guides
  • Registration Alerts — an email when your race opens registration, human-verified before sending
  • Guides and Comparisons — 60+ evidence-based training guides and 100+ head-to-head race comparisons
  • Developer Access — a free REST API and MCP server

Our Methodology

Every calculator on RunDida is grounded in peer-reviewed sports science and established coaching frameworks. Read our full methodology page for detailed formula documentation, validation processes, and source citations.

  • Pace and VDOT — based on Jack Daniels' Running Formula and VDOT tables
  • Heart Rate Zones — calculated with the Karvonen method (% of heart rate reserve)
  • VO2max Estimation — derived from the Cooper and Daniels regression models
  • Race Prediction — uses Riegel's formula with distance-specific adjustments
  • Calorie Estimation — based on MET research from the Compendium of Physical Activities

We cite our sources on every tool page so you can verify the science yourself.

Our Approach

  • Privacy First — all calculations run in your browser. No data is sent to our servers.
  • Mobile First — every tool is designed for phones first, then scaled up for desktop
  • No Account Required — use any tool instantly with zero sign-up friction
  • Always Free — no paywalls, no premium tiers

Credits

Food graphics on our nutrition tools are from Twemoji (© 2020 Twitter, Inc and other contributors), used under CC-BY 4.0.

Contact

Have a question, found a bug, or want to suggest a new tool? Send us a message and we will get back to you.