Health · 4 min read
How to Pick a Realistic Marathon Goal Time
The most reliable way to set a marathon goal is to start from a recent half marathon, run it through a prediction formula, and then adjust for how much training you've actually done. A common rule of thumb is to double your half marathon time and add 10 to 20 minutes. For a first marathon, erring towards the slower end is almost always the smarter call.
It's December, a lot of people are picking spring races right now, and the goal time you choose shapes every training run between now and April. So it's worth getting this bit right.
Method 1: Riegel's formula
Peter Riegel's formula predicts a time for a longer race from a shorter one:
T₂ = T₁ × (D₂ ÷ D₁)1.06
The 1.06 exponent is what slows you down as the distance increases. Here's what it gives for a few half marathon times:
| Half marathon | Riegel marathon prediction | Pace per km |
|---|---|---|
| 1:45:00 | 3:38:55 | 5:11 |
| 1:55:00 | 3:59:46 | 5:41 |
| 2:10:00 | 4:31:02 | 6:25 |
The pace calculator will do this for any time and distance, and show your splits.
Why the formula is often too optimistic
Riegel's formula assumes you're trained for the longer distance. For the marathon, a lot of recreational runners aren't quite. The last 10 km of a marathon is where limited long runs and low weekly mileage show up, and the formula can't see that. As a rough guide:
- Lots of training (several runs of 30 km+, consistent high weekly mileage): Riegel is a fair target.
- Moderate training (a few long runs up to 28–32 km, 40–55 km a week): add 5–10 minutes.
- First marathon or light training: add 10–20 minutes, or more.
That lines up with the "double it and add 10–20" rule. For a 1:55 half, that's a goal somewhere between 4:00 and 4:10.
Method 2: race your goal pace in training
Formulas are a starting point. Your training tells you more. A few weeks out, include some longer runs with marathon-pace sections, say 12–16 km at goal pace inside a longer run. If that feels controlled and your heart rate stays steady, the goal is realistic. If you're hanging on, knock a few minutes off your ambition now rather than finding out at 32 km.
Common goal paces
| Marathon goal | Per km | Per mile |
|---|---|---|
| 3:30 | 4:59 | 8:01 |
| 4:00 | 5:41 | 9:09 |
| 4:30 | 6:24 | 10:18 |
| 5:00 | 7:07 | 11:27 |
For more paces and distances, see the running pace chart.
Consider three goals, not one
Race day throws in weather, crowds, stomach issues and a bad night's sleep. Plenty of experienced runners go in with three targets:
- A goal: everything goes right. Maybe the Riegel number.
- B goal: a solid day. Probably your realistic target.
- C goal: finish healthy and enjoy it, especially on a hot day.
That way a warm, windy race isn't a failure; it's just a B or C day.
How to run the race itself
Whatever goal you pick, the way you pace it matters as much as the number. Starting 10–15 seconds per km faster than goal pace feels easy for the first 10 km and costs you badly after 30. Aim for even pacing or a slightly faster second half. We explain why in negative splits: how to pace a race.
And if it's your first marathon, remember that finishing is the real achievement. You'll have plenty of chances to chase a time once you know what the distance feels like.
Frequently asked questions
How do I predict my marathon time?
Use a recent half marathon time with Riegel's formula (T2 = T1 × (D2/D1)^1.06), then add time if your training volume is modest. Doubling your half time and adding 10–20 minutes is a common rule of thumb.
What marathon time does a 2-hour half marathon predict?
Riegel's formula predicts about 4:10:12, but most recreational runners with average training finish somewhere between about 4:10 and 4:30.
What pace do I need for a 4-hour marathon?
5:41 per km or 9:09 per mile, held for 42.2 km.
Should I have a time goal for my first marathon?
A rough goal helps with pacing, but it's smart to keep it conservative and treat finishing comfortably as the main aim.