Half Marathon to Marathon Predictor
Your half marathon time is the single best predictor of marathon performance. But simply doubling it won't give you an accurate estimate — the marathon's unique physiological demands mean the second half is fundamentally harder than the first. This predictor uses advanced scaling models to convert your half marathon into a realistic, honest marathon projection.
Quick answer: a 1:35:00 half marathon converts to about 3:29:14 for the marathon (typical range 3:22:22 to 3:38:53).
Half Marathon to Marathon conversion table
Estimates only – individual results vary with training, conditions and event experience.
| Half Marathon time | Predicted Marathon | Range |
|---|---|---|
| 1:05:00 | 2:23:09 | 2:18:28–2:29:46 |
| 1:09:00 | 2:31:58 | 2:26:59–2:38:59 |
| 1:13:00 | 2:40:47 | 2:35:30–2:48:11 |
| 1:17:00 | 2:49:35 | 2:44:02–2:57:24 |
| 1:21:00 | 2:58:24 | 2:52:33–3:06:37 |
| 1:25:00 | 3:07:12 | 3:01:04–3:15:50 |
| 1:29:00 | 3:16:01 | 3:09:35–3:25:03 |
| 1:33:00 | 3:24:49 | 3:18:07–3:34:16 |
| 1:37:00 | 3:33:38 | 3:26:38–3:43:29 |
| 1:41:00 | 3:42:27 | 3:35:09–3:52:42 |
| 1:45:00 | 3:51:15 | 3:43:40–4:01:55 |
| 1:49:00 | 4:00:04 | 3:52:12–4:11:08 |
| 1:53:00 | 4:08:52 | 4:00:43–4:20:21 |
| 1:57:00 | 4:17:41 | 4:09:14–4:29:34 |
| 2:01:00 | 4:26:29 | 4:17:45–4:38:47 |
| 2:05:00 | 4:35:18 | 4:26:17–4:48:00 |
| 2:09:00 | 4:44:07 | 4:34:48–4:57:13 |
How it works
The half-to-marathon conversion is one of the most studied relationships in running science. The model uses Riegel scaling with marathon-specific fatigue exponents, VDOT-based aerobic modeling, and glycogen depletion factors. The typical ratio is 2.09-2.15 (multiply half marathon by this factor), but it varies significantly based on your endurance profile, training volume, and marathon experience.
Training advice
Preparing for a marathon after running a half marathon requires building both volume and durability. Your peak long run should reach 32-35 km. Practice marathon-pace running in dedicated sessions (15-25 km at goal pace). Fueling becomes critical — practice your nutrition strategy in every long run. Most runners need 16-20 weeks of marathon-specific training after establishing a half marathon base.
Frequently asked questions
Can I just double my half marathon time for a marathon?
Doubling is a starting point, but most runners should add 8-20 minutes to the doubled time. The exact amount depends on your endurance profile, training, and marathon experience. Our predictor uses more sophisticated models than simple doubling.
What is the half marathon to marathon ratio?
For well-trained runners, the ratio is typically 2.09-2.12. For recreational runners or those newer to the marathon, 2.15-2.22 is more common. Elite runners with exceptional endurance may see ratios as low as 2.04-2.08.
Is a marathon more than twice as hard as a half marathon?
Physiologically, yes. The marathon pushes you into glycogen depletion territory, which doesn't happen in a half marathon. The last 10 km of a marathon are uniquely challenging because your body is running on increasingly limited fuel stores.
How many half marathons should I run before a marathon?
There's no fixed rule, but completing 2-3 half marathons gives you valuable racing experience. More important than the number is having a strong training base — consistent weekly mileage and long runs matter more than race experience.
Related tools
- Marathon Time Predictor
- Half Marathon Time Predictor
- How to Predict Marathon Time
- Negative Split Calculator
- Running Pace Calculator