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The maths,
done for you.

17 calculators built alongside 220 hand-researched race guides — so the numbers you get out are the ones that matter for the race you're actually entering. Every one is free and works without signing up.

17
Calculators
£0
Forever

What pace should I run?

Turn a target time into the pace you actually have to hold, and see it broken into checkpoint splits.

Running Pace Calculator Solve pace, time or distance — instantly, for any race. Marathon Pace Chart Every common finish-time band, one table. Swim Pace Calculator Pool, open water, or a triathlon swim leg — one converter. Triathlon Split Calculator Your own swim, bike and run pace — one projected finish time. Treadmill Pace Converter What your belt speed and incline are actually worth outside.

What am I capable of?

Use a recent result to estimate what you could run at another distance, set training paces from it, and see the aerobic capacity behind it.

Race Time Predictor A recent 5K or 10K tells you more than you think. Training Pace Calculator One race result, five training paces. VO2 Max Calculator Your aerobic ceiling, estimated from a race rather than a lab.

What will race day be like?

The conditions you can know in advance — and the rules that decide what you are allowed to wear.

Heat-Adjusted Pace Calculator What the weather will cost you — as a range, not a false promise. Triathlon Wetsuit Calculator Know before you pack it — for any venue on earth.

What do I need to take on?

Fluid, sodium and carbohydrate, measured from your own body rather than estimated from a population average.

Sweat Rate Calculator Measured, not estimated — because no formula knows how much you sweat. Race Fuel Calculator Carbs, fluid and sodium for the race you are actually running.

How long do I need to train?

Four starting points, not one — pick where your training actually is and get a real number of weeks, from a 5K to a full-distance Ironman.

5K Training Duration Calculator From your first run to your first 5K — the real timeline. 10K Training Duration Calculator From your first run to race day — the real number of weeks. Half Marathon Training Duration Calculator From a standing start to race-ready — the real timeline, not the generic one. Marathon Training Duration Calculator Four starting points, one honest number of weeks. Ironman Training Duration Calculator 70.3 or full distance — the real timeline for three disciplines at once.

Why these aren't the usual calculators

The formulas are stated

The race time predictor uses Riegel's formula and says so. The training paces are computed from Daniels-Gilbert equations rather than copied from a table. If you want to check the maths, we tell you what maths to check.

They know your actual race

Each tool links straight into the race guides it's useful for — so a pace chart isn't generic, it sits next to the elevation, cut-off and start time for the race you're entering.

Nothing is invented

Where a figure genuinely is not published — an elevation, an entry fee, a start time — the tools and guides say so rather than estimating and presenting the estimate as fact.

Read the thinking behind them

A calculator gives you a number. These explain what to do with it.

All 116 guides
Running in Jamaica's Heat: What It Actually Costs You Where to Run in Kingston: The Routes Locals Actually Use Running in Jamaica as a Visitor: A Practical Guide Open Water Swimming in Jamaica: What the Sea Is Actually Doing Triathlon in Jamaica: The Races, the Scene and What to Expect

Common questions

How much slower should I run in the heat?

It depends on both temperature and humidity together. As a guide, add air temperature and dew point in Fahrenheit: under 100 there is no real penalty, 120–130 costs roughly 1–2%, 140–150 costs 3–4.5%, and above about 165 the honest answer stops being a percentage and becomes a question of whether to race at all. This calculator does that sum for you and applies the range to your goal pace.

Why does dew point matter more than humidity?

Relative humidity is relative to temperature, so 80% humidity means something very different at 5°C than at 30°C. Dew point is an absolute measure of how much moisture the air holds, which is what actually determines whether your sweat can evaporate and cool you. Two mornings with the same relative humidity can be completely different runs; two with the same dew point rarely are.

Does the heat penalty affect a 5K as much as a marathon?

As a percentage the bands are similar, but the cost in real time scales with how long you are out there — and the longer you run, the more heat accumulates. A 3% penalty is about nine seconds on a 5K and roughly seven minutes on a marathon. Expect to sit nearer the upper end of the band for longer races.

Does acclimatising to heat actually help?

Yes, and it is one of the best-established adaptations in the sport. Ten to fourteen days of training in the heat produces measurable changes — more plasma volume, earlier and more dilute sweating, a lower heart rate at the same effort. It reduces the penalty rather than removing it, which is why this tool moves you to the better half of the same band instead of pretending the heat has gone.

Why does this give a range instead of a time?

Because a range is what the underlying rule actually supports. It is a coaching heuristic derived from race-day observation, not a validated physiological model, and individual variation is wide — two runners in the same race and the same conditions routinely differ by more than the width of a band. A tool that told you 3:47:22 would be inventing precision, and runners plan races around numbers like that.

When is it too hot to race safely?

There is no single threshold, but once air temperature plus dew point passes roughly 165°F, races are commonly shortened, cancelled or moved. At that point heat illness is the risk rather than a slow finish time, and it is a medical emergency rather than a pacing problem. Chills, stopping sweating, or confusion mean stop and get help, not push on.

How do I calculate my running pace?

Pace is your total time divided by distance. This calculator does that automatically — enter a target finish time and distance, and it shows your required pace per mile and per km, plus splits at each checkpoint.

What is a good running pace for a beginner?

It varies hugely by fitness and goal, but a common beginner marathon target is 5:30-6:30/km (roughly 9:00-10:30/mile), often run with run/walk intervals. Use the calculator to see what finish time your current pace would produce, then work backward from there.