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Race Weather & Heat Adjustment Calculator

Tools · Race Weather Calculator

Race Weather & Heat Adjustment Calculator

Heat and humidity slow everyone down — even runners who've trained perfectly. The trouble is most people don't adjust their goal pace for it, then blow up in the back half. Enter the forecast for your race morning and your goal pace, and I'll estimate how much conditions are likely to cost you, so you can start smart instead of chasing a number the weather won't let you hit.

Work out your heat-adjusted pace

Use the forecast for race morning, not right now — conditions at an 8am start are usually very different to a 2pm check.

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Enter the forecast conditions and your goal pace, then hit calculate.

This is a practical planning guide, not a medical or meteorological tool — real heat impact varies by fitness, heat acclimatisation, course shade and individual sweat rate. In genuinely extreme conditions, prioritise safety over goal times: slow down, hydrate, and consider walking through aid stations.

How to use the heat adjustment calculator

Enter the forecast temperature and humidity for your race start time, pick whether it'll be sunny or shaded, and enter your goal pace. You'll get a heat-stress risk flag, your heat-adjusted pace, and a table showing how much time that adds across 5K, 10K, half marathon and marathon distances.

Treat the result as a planning guide, not a guarantee — heat tolerance varies a lot by individual, and acclimatisation, fitness and course shade all play a part. In genuinely extreme conditions, the smart move is to let go of your goal time altogether: slow down, hydrate, and treat the day as a training run rather than a PB attempt.

Want to build a pacing strategy around this adjusted number? Try the Pace Calculator or the Race-Day Split Planner. Or if you'd like a coach in your corner for race-day strategy generally, take a look at bespoke training plans or online coaching, or get in touch for a free, no-pressure chat.