Free running calculators
Run the numbers.
Then run the race.
Pace, race-time prediction, VDOT training paces, splits, and age-graded scoring: five free calculators, no login required. Connect Strava, Whoop, or Garmin later for a version personalised to your actual training.
Five free calculators
Every calculator runs entirely in your browser. Nothing you enter is sent anywhere or stored.
Pace Calculator
Enter any two of pace, time, and distance to solve for the third.
Race Time Predictor
Predict equivalent race times at other distances from one recent result.
VDOT / Training Pace Calculator
Get your Daniels & Gilbert VDOT and suggested training paces.
Split Calculator
Build an even- or negative-split pacing table for a goal time.
Age-Graded Performance Calculator
Score a performance against WMA age-grading factors.
Beyond generic formulas
The free tools use standard published formulas. Connect a provider and Slow Run Fast swaps those generic estimates for numbers grounded in your own training history.
Strava
Sync runs automatically and see your real training load behind every number.
Whoop
Layer in recovery and strain so pacing advice accounts for how your body is actually doing.
Garmin
Import files directly for splits, HR zones, and power data the free tools can't see.