Does it support hilly courses?

Use the environmental adjustment and add buffers. For extreme net uphill/downhill courses, tweak the exponent or set a manual time.

What format is the split chart?

Splits for 1 km/mile checkpoints are displayed in a table and can be exported as CSV for Google Sheets or Excel.

Race Predictor

Forecast marathon, half, and 10K goals, then export the plan you’ll actually execute.

Q: Can I use a non-peak race?

Yes. If the input race was under heavy fatigue or in hot weather, adjust the time or exponent to match current fitness.

Input one recent finish time to project new goals, apply weather and elevation adjustments, generate pacing charts, and estimate fueling needs. The calculator keeps your stretch time ambitious yet achievable.

Start predicting Browse 2025 races

Riegel projections Translate a recent PR into marathon, half, and 10K targets instantly.

Weather-aware Adjust for heat, humidity, altitude, and wind before race day surprises you.

Splits & fueling Export km/mi splits and calculate hourly carbs, sodium, and fluids.

🏁 Race prediction & goal pace

Predict a target race or lock in a manual goal time to see required pace, splits, and fueling guidance instantly.

Recent result

Distance

Finish time

Target race

Distance

Goal time (leave blank to predict)

Predicted/goal finish

—

Required average pace

— min/km

Marathon presets:

Half-marathon presets:

Advanced Riegel exponent

Tip

Use 1.03–1.04 for aggressive pacing, 1.06 default, and 1.07–1.08 for conservative endurance-focused attempts.

Weather adjustment

Temperature (°C) Humidity (%) Elevation (m) Wind (m/s)

Adjusted time: —

Fuel & hydration

Body weight (kg) Carb intake (g/h) Sodium (mg/h) Fluid (ml/h)

Total carbohydrate: — g (≈ — gels)

Total sodium: — mg, fluids: — ml

Estimated calories: — kcal

Training pace guide

• Easy: — /km (— /mile)
• Marathon pace: — /km (— /mile)
• Tempo (half): — /km (— /mile)
• Threshold (10K): — /km (— /mile)
• Intervals (5K): — /km (— /mile)

Weekly 80/20 planner

Weekly mileage (km)

Easy (80%): — km, Quality (20%): — km

Interval session planner

Template

Rep pace

— /km

Rep time: —, Rest: —

FAQ

Can I use a non-peak race?

Yes. If the tune-up race was under tough conditions or heavy shoes, adjust the exponent or subtract a few minutes before predicting.

How should I use the CSV?

Import it into Google Sheets to annotate fueling, hydration, or spectator support points. Print a pace band or share with teammates.

Start predicting →

Core terms

Riegel exponent: A baseline 1.06 exponent that models how finishing times slow as distance increases; tweak it to reflect your endurance profile.
Environment adjustment: Applies heat, humidity, altitude, and wind penalties so predicted pace matches real-world race day conditions.
Split CSV: A downloadable table of km/mile checkpoints you can drop into spreadsheets, pace bands, or your watch.

Suggested playbook

12-week build — Anchor marathon pace with your latest 10K, keep 80% of mileage easy, and layer tempo/LT efforts in the final 8 weeks.
Heat adjustments — If race-day temps exceed 68°F (20°C), widen the prediction by 1–2% or lower the Riegel exponent for realism.
Fuel & hydration — Translate hourly carbs/sodium to gels and bottles, then map them to aid stations before taper week.

Companion tools

Rehearse goal pace indoors Update LT pace & HR Check upcoming race dates