How quickly do you lose running fitness?

You lose about 3-5% of aerobic fitness per week of inactivity for the first 4 weeks. After 8+ weeks off, you may retain only 50-70% of your previous fitness.

Should I use walk-run intervals when returning?

Yes, walk-run intervals are an excellent strategy for returning from injury or illness. Start with 1-2 minute run intervals with 1-2 minute walks between.

What is the 10% rule for increasing mileage?

The 10% rule suggests increasing weekly mileage by no more than 10% each week. This allows your body to adapt and reduces injury risk during build-up.

When should I see a physio before returning?

If your time off was due to a specific injury, get clearance from a physiotherapist before returning. If pain returns during your comeback, stop and seek advice.

RunCalcs

Return to Running Calculator — Safe Comeback Plan

Plan a safe return-to-running schedule after time off or injury.

Weeks Off

Previous Weekly Distance

Reason for Break

How We Calculate This

Return to Running Protocol

This calculator uses a graduated return based on the 10% weekly increase rule:

Starting Volume = Previous Weekly km x Start Percentage

Start percentages vary by reason: injury (40%), illness (30%), general break (50%).

Weekly increases of 10% are applied until you reach your previous volume. Every 3-4 weeks, include a step-down week at 80% for consolidation.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always consult a coach or medical professional for personalised training advice.