marathonpacecalc.com
Predict your finish time and splits for any race distance — free and instant.
Predicted finish time
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Checkpoint splits
Choose between two modes: Calculate pace if you know how fast you want to run and need your predicted finish time, or Predict from race if you have a recent race result and want to know how that translates to a longer or shorter distance.
Both modes display checkpoint splits at key points in your race — giving you a clear pacing plan before you even reach the start line.
Select your target distance (5K, 10K, half marathon, or full marathon), enter your goal pace in minutes and seconds per kilometre or per mile, and the calculator instantly shows your predicted finish time. Checkpoint splits are displayed at key distances so you know exactly where you should be at every stage of the race.
This mode is ideal for runners who already have a target pace in mind — for example, aiming for a sub-4:00 marathon (5:41/km) or a sub-2:00 half marathon (5:41/km).
Enter a recent race result — any distance from 5K to full marathon — select your target distance, and the calculator predicts your finish time using the Riegel formula. This is the same method used by Runner's World, the London Marathon official pace calculators, and most serious race prediction tools worldwide.
The Riegel formula (T2 = T1 × (D2 ÷ D1)^1.06) accounts for the natural slowdown in pace as race distance increases. Unlike a simple linear calculation, it understands that running a marathon is disproportionately harder than running a half marathon — and adjusts accordingly.
Splits show your predicted cumulative time at key checkpoints through the race. For a marathon, you will see predicted times at 5K, 10K, the halfway point (21.1km), 30K, and the finish. For a half marathon, splits are shown at 5K, 10K, 15K, and the finish.
Use these splits as a pacing guide on race day. Print them out, write them on your wrist, or programme them into your GPS watch. Arriving at each checkpoint within a few seconds of your predicted split time means you are running a well-controlled race.
If you reach the 10K mark significantly ahead of your predicted split, slow down — you are burning glycogen faster than planned and will likely pay for it in the second half.
The Riegel formula is highly accurate for distances from 5K to half marathon when the reference race is recent and run at full effort. For full marathon predictions from shorter distances, accuracy depends on several factors including training mileage, long run experience, and race-day conditions.
Runners who have completed multiple long runs of 18 miles or more and have trained specifically for the marathon distance will typically finish within 5 to 10 minutes of their prediction. Runners stepping up to their first marathon from a half marathon background may find the actual time is 10 to 20 minutes slower than predicted, particularly if their long run training has been limited.
For the most accurate prediction, use a race result from a similar distance to your target — a half marathon result predicts a marathon time more accurately than a 5K result.
The most common mistake in marathon running is going out too fast. Research consistently shows that runners who start conservatively — even 10 to 15 seconds per kilometre slower than goal pace for the first 10K — finish faster overall than those who run even splits or positive splits.
A negative split strategy (running the second half faster than the first) is the hallmark of elite marathon running. At the London Marathon, the majority of age-group PBs are run with a negative or even split. Use your predicted splits as a ceiling in the first half, not a target.
The 30K mark is where most marathon races are won or lost. Runners who have paced sensibly in the first half will have glycogen reserves to maintain pace through the final 12 kilometres. Those who went out too fast will hit the wall — the point at which glycogen stores are depleted and pace drops sharply.
Your marathon goal pace should only appear in your training during specific marathon pace workouts — typically medium-long runs at goal pace, or the final miles of a long run. The majority of your training mileage should be run significantly slower.
As a general guide, your easy running pace should be 60 to 90 seconds per kilometre slower than your marathon goal pace. For a runner targeting a 4:30 marathon (6:24/km), easy runs should be at approximately 7:15 to 7:45/km. Running your easy days too fast is the single most common cause of overtraining and injury in marathon preparation.
Tempo runs — sustained efforts at a comfortably hard pace — should sit roughly 20 to 30 seconds per kilometre faster than marathon goal pace. Interval sessions can be significantly faster, depending on the session design.
5K = 5 kilometres (3.1 miles) — typically completed in 20 to 40 minutes by recreational runners. A popular parkrun distance and an excellent benchmark for shorter race predictions.
10K = 10 kilometres (6.2 miles) — double the 5K distance. A 10K result is one of the most reliable predictors of half marathon and marathon performance when used with the Riegel formula.
Half marathon = 21.1 kilometres (13.1 miles) — the most popular long-distance race in the world. A well-run half marathon in the 12 weeks before a marathon is the strongest possible predictor of marathon finish time.
Marathon = 42.195 kilometres (26.2 miles) — the classic distance. Named after the Greek messenger who ran from Marathon to Athens in 490 BC. First included in the modern Olympics in 1896. Today completed by millions of runners worldwide each year across thousands of events.
Can I use my parkrun time to predict my marathon? Yes — enter your parkrun time as a 5K result in the Predict from race mode and select marathon as your target distance. The prediction will be reasonable but less accurate than using a half marathon result, particularly if you are new to longer distances.
How do I convert pace per mile to pace per kilometre? Divide your per-mile pace in seconds by 1.60934. For example, an 8:00/mile pace (480 seconds) converts to 480 ÷ 1.60934 = 298 seconds = 4:58/km. Our calculator handles this conversion automatically.
What is a good marathon time? For a first-time marathon runner, finishing is the primary goal. The average marathon finish time worldwide is approximately 4 hours 30 minutes. Sub-4:00 is a common intermediate goal. Sub-3:30 represents a strong club runner. Sub-3:00 is competitive at most age group levels.
How long should I train for a marathon? Most standard marathon training plans run for 16 to 20 weeks. First-time marathoners benefit from a longer build, while experienced runners with a solid base can follow a focused 12-week plan.