Predict your 26.2-mile finish time from a recent race result or your current training pace.
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Choose your input method from the three tabs: enter a recent race result (5K through half marathon), input your current training pace per mile, or use any custom race distance. Fill in your time, select the prediction formula or experience level, then click Predict My Marathon Time. You'll see your projected finish time, per-mile pace, your performance zone on a color-coded bar, and a full 5K split breakdown.
Setting a realistic goal time is one of the most important decisions you'll make before race day. Go out too fast and you'll hit the wall — that dreaded crash around mile 18–20 where glycogen runs out and pace collapses. Go out too slow and you leave time on the table after months of training.
Consider this: a runner who finishes a half marathon in 1:55:00 is predicted to finish a full marathon in approximately 3:59–4:05. But a first-timer with the same half time, due to less race-specific endurance and pacing experience, often finishes closer to 4:15–4:25. The difference is very real — and very trainable.
Coaches, pace groups, and training plans all rely on time predictions to set workout targets. Your predicted marathon pace becomes your "goal marathon pace" (GMP), which drives your tempo runs, long run efforts, and race-day strategy. Using a scientifically-grounded predictor — rather than gut feel — gives you a number you can trust and build a race plan around.
This tool also shows your performance zone: whether you're on track for a Boston Qualifier, a sub-4, a sub-5, or simply your best personal effort. Knowing where you stand helps you pick the right corral and the right mindset.
Riegel Formula (default): T₂ = T₁ × (D₂ / D₁)^1.06 — where T₁ is your known race time, D₁ is that race distance, D₂ is 42.195 km, and 1.06 is the fatigue exponent. This exponent reflects that longer races feel disproportionately harder.
Cameron Formula: Uses a slightly different exponent curve that some researchers argue better fits recreational runners: T₂ = T₁ × (D₂/D₁) × [(a + b × D₂) / (a + b × D₁)] with empirically derived constants.
Training Pace Method: Your long run pace is multiplied by an experience factor (1.06–1.18) and a training completeness factor based on weeks trained. The result is your predicted marathon pace, then multiplied by 26.2188 miles (full marathon distance).
The 5K splits assume an even-effort pacing strategy — the single most effective race plan for first-time finishers and those chasing a PR.
For runners who have trained consistently and raced the reference distance near full effort, Riegel is typically accurate within 3–7 minutes for most recreational runners. Elite runners tend to fall within 1–2 minutes. The accuracy drops when using very short reference races (5K) or when the runner is new to the marathon distance.
Yes, but with caution. A 5K covers such a short distance that small variations in fitness, course, and effort create larger prediction errors at 26.2 miles. Use the result as a rough guide and round up by 3–5 minutes to be conservative, especially if you haven't done marathon-specific long runs.
Boston Qualifying times vary by age and gender — for men 18–34 it's 3:00:00, rising to 3:10 for 35–39, and so on; women's standards are 30 minutes slower per age group. Note: due to high demand, the actual cutoff is typically 2–6 minutes faster than the published standard. Check the BAA website for current standards.
Different calculators use different fatigue exponents and correction factors. The Riegel exponent of 1.06 is the most commonly cited, but some tools use 1.07–1.08 for more conservative estimates. Try all three formula options in this tool — your true finish time will likely fall within that range.