How to Adjust Your
London Marathon
Pace for the Conditions

Six years of finish-time data reveal exactly how temperature changes pace for every ability level — from sub-2:30 elites to 5h+ runners.

How will conditions affect your finish time?

Enter your target time under good conditions (≈ cool, calm day), the forecast temperature, and any expected wind. The calculator uses historical London Marathon data to project how much slower you should expect to be.

When it's hot, everyone slows down

Each band shows the range of finish times for a given percentile of runners. The top of the chart (p90–p95) is the slowest runners; the bottom (p5–p10) captures the sub-3h zone. Both shift dramatically upward in 2018's 20°C heat.

The hotter it is, the bigger the fade in the second half

Slowdown % = how much slower the second half was vs the first half. Each of the 98 bands represents a 1-percentile slice of all runners.

Do men and women respond differently to heat?

Comparing the p10, p50, and p90 slowdown lines for male (blue) and female (pink) runners at the same percentile rank within each group. A gap between lines would indicate one gender suffers more from heat.

London's course runs WNW. Most years face a headwind

The London Marathon runs net west-northwest (Blackheath → The Mall, bearing ≈295°). A true tailwind would come from ESE (115°). The chart below shows the course-aligned wind component for each year. Negative = headwind into runners' faces.