70.3 Time to Ironman Time: What the Race Data Says

70.3 time to full Ironman time: the short answer

To turn a 70.3 time into a full Ironman time, double it and add about 30 minutes. That is what I got when I divided the typical full Ironman finish by the typical 70.3 finish in my race results database. The ratio comes out at 2.08, so a 6:00 half lines up with a 12:29 full. The old rule of thumb, double it and add an hour, gives 13:00, which is about half an hour slower than the typical full.

I wanted to check that rule because every forum thread I found about it was from 2007 or 2008, and I couldn't find anyone who had checked it against real results. I took the age-group medians from my average 70.3 finish time post and my average Ironman finish time post, divided one by the other, and then looked at five towns that host both races. Below are the ratios for every age group, the town check and a table you can read your own time from. The ratio compares two fields and is not a promise for one athlete. It can't tell you how your first full will go, and I say why near the end.

Does double it and add an hour hold up?

The two Slowtwitch threads I read give a handful of rules. In 2007 one poster wrote twice the half plus an hour, and another said plus one to two hours, with first-timers toward the two. In 2008 the replies were double plus 30 minutes, double plus 20 percent, or double give or take an hour. One poster said no formula works at all.

So I tried the simplest version on the typical race. The typical 70.3 median is 6:00 and the typical full median is 12:28, a ratio of 2.08. The ratio barely moves as you go through the field.

The fast end and the slow end sit at about the same 2.1. Double plus an hour is 23 to 32 minutes too slow in every row. If I had to pick a simple rule from this, I'd say double it and add half an hour. For a 5:00 half that gives 10:30 and for a 7:00 half it gives 14:30, close to what the ratio says.

The ratio by age group, men and women

I did the same division for every age group, using the medians in my two finish-time posts. The last column shows how far off double plus an hour would be.

Two things stood out. From 25 to 39 the ratio is 2.06 or 2.07 for both men and women, and the old rule runs 35 to 39 minutes slow. For men the ratio then climbs with age, to 2.14 at 50 to 54 and 2.18 at 60 to 64. For men over 50 the old rule is nearly right, within 11 minutes.

I can't say why. Older men might slow down more over 226 km than over 113, or the people who sign up for each distance might just be different. Women don't show a clean climb, so I wouldn't read much into the wobble at 40 to 44 and 50 to 59.

The same town test: five 70.3 and full pairs

The two distances have different fields, so I also looked for towns where both races are on my race pages. Five came up. This is the median finish at each. You can open the race pages for Cairns (full, 70.3) and Vichy (full, 70.3).

The ratio runs from 1.95 at Cozumel to 2.10 at Vichy and averages 2.04. Double plus an hour is too slow at all five, by 22 minutes at Vichy and 80 at Cozumel. I don't know why Cozumel is so low. Five towns are too few to say much more than this: the ratio moves around by 0.15, which is close to an hour on a 6:00 half. That is why I'd treat 2.08 as a middle and not a promise.

Where the extra eight percent goes

Each leg of a full Ironman is exactly twice as long as at a 70.3, so a ratio above 2 means a slower pace. My swim, bike and run times post has the typical legs for 117 70.3 races and 43 full races. Dividing one by the other gives this.

The swim takes twice as long, the bike a little more and the run a lot more. The typical full run is about 31 minutes slower than two 70.3 runs back to back, and the bike is about 11 minutes slower than two. That is about 41 minutes over double, a bit more than the half hour from the finish times. The two come from different sets of races.

A full Ironman time from your 70.3 time

This is the lookup. The second column is the old rule. The third uses the 2.08 ratio from all races. The last spans the lowest and highest ratio from the five towns, 1.95 to 2.10.

Use the third column as the typical number and the last as the range. Men over 50 sit nearer 2.15 in my tables, which puts them closer to the old rule. If you want a number for a particular race, the race time estimator works from that race's own results.

What this can't tell you

This compares two fields, not one athlete. The people who race a full Ironman are not the same people who race a 70.3, and I haven't matched athletes from one race to the other.

It also says nothing about a first full. One poster in the 2007 thread thought first-timers lose more time, and I can't confirm that, because race results don't show who is doing their first one.

And the course swamps all of it. In my finish time post the typical full runs from 11:08 at Ironman Brazil to 14:17 at Ironman Philippines, a gap of more than three hours. A 6:00 half in one town doesn't promise a 12:29 full in another. To see which full courses run quick, look at the easiest Ironman courses and the hardest Ironman courses. If you are still on the 70.3 side, I wrote about how to choose your first 70.3.

About the data

• Each ratio divides an age-group median from my average Ironman finish time post (41 full races, about 65,000 finishers) by the same group's median from my average 70.3 finish time post (121 races, about 176,000 finishers). Both use the latest 2025 or 2026 edition of each race and leave out the World Championship races.
• The medians describe a typical race, not a pooled list of finishers. The ratio compares two fields and says nothing about one athlete.
• Times in those posts are rounded to the minute, so the ratios are rounded too. 'Off by' is double plus an hour minus the typical full.
• The town pairs come from the public race pages, read on 14 November 2026. I used the median finish of the latest edition shown. The Cozumel full is 2025 and its 70.3 is 2026, and both Western Australia races are 2025.
• The swim, bike and run table uses my swim bike run times post, which has a slightly different set of races (117 and 43), so its legs don't add up to the finish times.
• Only finishers count, so a race with many DNFs can look quicker than it was. There is no full median for women 70 and over, so that group is left out. Men 70 to 74 come from 36 full races.
• The rules of thumb come from two Slowtwitch threads, from 2007 and 2008, which I read on 14 November 2026. I paraphrased them.