What is bonking in cycling?

Bonking (or hitting the wall) occurs when glycogen stores are depleted. Symptoms include sudden fatigue, dizziness, inability to maintain power, confusion and sometimes nausea. It feels like your legs are made of concrete.

How long can I ride without eating?

For most trained cyclists at moderate intensity, glycogen lasts 90-120 minutes. At race pace, stores deplete in 60-90 minutes. Easy riding can be sustained for 2-3 hours without food.

How do I prevent bonking?

Start fuelling from the first hour: aim for 30-60g of carbs per hour (60-90g for trained riders in long events). Eat before you feel hungry — by the time you feel depleted, it is too late.

Does carb loading help?

Yes. Proper carb loading (8-10g/kg/day for 2-3 days before an event) can increase glycogen stores by 50-100%, significantly delaying the bonk point.

Can you recover from a bonk during a ride?

Yes, but slowly. Consume fast-acting carbs (gels, sugary drinks, sweets). It takes 15-30 minutes to feel the effect. You will not fully recover to normal performance during the ride.

Bonk Calculator — When Will You Hit the Wall?

Estimate when glycogen stores will deplete without fuelling during a ride.

Body Weight

Your body mass — larger riders store more glycogen but also oxidise more carbohydrate

Ride IntensityHow hard the ride feels relative to your zones — harder efforts burn carbohydrate far faster

Fitness LevelEndurance training raises muscle glycogen density, so fitter riders hold out longer

Hours Since Last Meal

Time since your last carbohydrate-containing meal — a longer gap means lower starting glycogen

Last Meal SizeApproximate carbohydrate content of your pre-ride food — bigger carb meals top up glycogen

How We Calculate This

Glycogen Depletion Model

Usable leg glycogen: ~500-950 kcal depending on fitness and body weight. The wall is driven by working-muscle glycogen — liver glycogen spares the brain, not the legs — so this limiting pool is what counts, not whole-body stores.
Pre-ride meal tops up glycogen by 100-600 kcal; each hour since eating drains ~20 kcal of glycogen (net hepatic depletion ~4-7 g/h).
Carbohydrate oxidation rises steeply with intensity: ~1.0 g/min easy, ~2.0 g/min (120 g/h) moderate, ~3.0 g/min hard, ~3.5 g/min at race pace (×4 kcal/g), scaled by body mass.
Bonk time = usable glycogen ÷ carbohydrate burn rate. At moderate steady intensity a trained rider hits the wall at ~90-120 minutes; at race pace ~60-90 minutes.
Fuelling warning = 70% of bonk time by default (adjustable), so you start eating well before the wall.

Frequently Asked Questions

Last updated: February 2026

All calculations are estimates. Always verify results and consult a professional bike fitter where appropriate.

Bonk Calculator — When Will You Hit the Wall?

How We Calculate This

Glycogen Depletion Model

Frequently Asked Questions

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