The marathon is 42.195 kilometres of calculated effort. Getting pacing wrong — even by 10–15 seconds per km — leads to the dreaded slowdown after 30km. Use this calculator to find the exact pace per km or mile for any target finish time, predict your marathon potential from recent race results, and build your training zones around your goal race.
Preview
Essential for first-time marathon runners setting a realistic target pace, experienced runners calculating splits for a personal best attempt, and coaches building race-day pacing strategies. Also useful for runners deciding whether their training suggests they are ready to target a specific finish time.
Divide your target marathon finish time by 42.195 to get pace per kilometre. This calculator does that instantly and also converts to per-mile pace — useful if your watch or race markers are in miles.
The Riegel race predictor (T2 = T1 × (D2/D1)^1.06) estimates your marathon from a half marathon or 10K. It accounts for the disproportionate fatigue at longer distances. Predictions are most reliable when based on a recent half marathon run at race effort.
Marathon training pace zones are set conservatively: easy long runs at 65–75% of max pace, marathon race pace at 80–85%, and tempo intervals at 85–90%. Staying in the right zone prevents over-training in the build-up phase.
First marathon goal: finish in 4:30
Inputs: Distance: 42.195 km, Time: 4:30:00
Pace: 6:24/km (10:18/mile). Each kilometre should take approximately 6 minutes 24 seconds.
Target sub-4 hour marathon
Inputs: Distance: 42.195 km, Time: 3:59:59
Pace: 5:41/km (9:09/mile) — identical per-km pace to a sub-2-hour half marathon.
Predict marathon from half marathon PB
Inputs: Half marathon: 1:55:00 (use as 21.1km reference)
Predicted marathon: approximately 4:00:00–4:05:00 for a well-trained runner.
A 4-hour marathon requires averaging 5:41/km (9:09/mile) for 42.195km. That means every kilometre marker should show approximately 5:41 on your watch. Many runners use a strategy of 5:45/km for km 1–10, 5:40/km through km 11–30, and race on feel for the final 12km.
The wall is primarily a fuelling and pacing problem. Running the first half too fast burns glycogen too quickly. Aim to run the first 21km at target pace or 5–10 seconds slower, take on carbohydrate every 30–45 minutes from km 10 onwards, and conserve enough energy for km 30–42.
Yes. Multiply your half marathon time by 2.1 for an optimistic estimate or 2.15 for a more realistic one. This calculator uses the Riegel formula, which gives a precise projection. A 2:00 half marathon predicts a marathon of approximately 4:10:00–4:20:00 depending on training volume.
A negative split means running the second 21km faster than the first. Most marathon world records are run with near-even or slightly negative splits. For recreational runners, even splits are more achievable — the key is avoiding a positive split where the second half is significantly slower than the first.
Most marathon training plans peak at 60–80km per week for intermediate runners. The long run typically reaches 30–32km three weeks before race day. Weekly mileage matters more than single long run distance — consistent training volume across 16–20 weeks produces better marathon results than last-minute high-volume training.