Free calculators for runners and cyclists

Pick the question you have. Most take a minute, need no account and keep your inputs in your browser.

5 calculators

Example: a 20:00 5K

5Kinput: 20:00
10K: 41:42
Half marathon: 1:32:00
Marathon: 3:11:49
Marathon, Garmin-implied: 3:43:11

Running · 1 min · Free

Race pace predictor

What could I run at another distance?

One recent result becomes finish times and paces from one mile to 50K, on two curves.

You bring: One race time
You get: Finish times and paces

Open the calculator

Example: age 40, max 180 bpm (220 − age)

Zone 5: 162–180
Zone 4: 144–162
Zone 3: 126–144
Zone 2: 108–126
Zone 1: 90–108

Running and Cycling · 1 min · Free

Heart-rate zones

Where does easy actually end?

You bring: Age, or max and resting heart rate
You get: Five zones on three models

Open the calculator

Example: 2,800 m in a 12-minute Cooper run

ml/kg/min

Point estimate. The tool shows the range around it.

Running · 2 min · Free

VO2 max estimator

How large is my aerobic engine?

You bring: One field test
You get: A VO2 max range

Open the calculator

Example: 250 W held for 20 minutes

The ×0.95 textbook conversion, split into seven power zones.

Cycling · 1 min · Free

FTP estimator

What power could I hold for an hour?

You bring: Test duration and watts
You get: FTP range and power zones

Open the calculator

Example input: weekly training stress

Week 1: 300
Week 2: 350
Week 3: 450
Week 4: 250

Running and Cycling · 2 min · Free

Training load calculator

Am I building fitness or only fatigue?

You bring: Four weeks of TSS
You get: Fitness, fatigue and form

Open the calculator

Zones by age

Heart-rate zones already worked out for your age.

Simple inputs, visible assumptions

The metrics explained The research

Private by default

Nothing is uploaded or saved.

Ranges, not false precision

Every result shows its uncertainty.

Sources named

Every formula says where it comes from.