How Long to Train for a First Ultramarathon¶
The weeks matter less than where you start. The rule passed around ultra circles goes like this: be able to run in a week what you will run on race day, and hold that for the twelve weeks before the race. Count back from there to the week you are in now.
The rule gets credited to David Horton. He taught an advanced running course at Liberty University for 46 years, and his students were required to finish a race of 50K or longer. I have not found it written down in his words, so take it as how the community passes it on, not as a quote.
Here is what it means for a 50K, which is about 31 miles. Run 31 miles in a week, and keep running about that much for twelve weeks. Then taper and race. That is the rule as it gets passed around.
Two parts of that are doing the work. One is the number, which is the race distance. The other is the twelve weeks, which is long enough that the number stops being a peak you touched once and becomes something your legs know.
How long should I train for a 50K?¶
Twelve weeks of holding the number, plus however long it takes to get to the number.
That second part is the one nobody puts in the plan title. A "12 week 50K plan" assumes you already run close to the race distance each week. If you do, twelve weeks is the whole answer. If you do not, you have a ramp in front of the twelve.
An example, with made-up numbers. Say you run 20 miles a week now, from a couple of half marathons and some trail days. The target is 31. That is 11 miles to add. If you add 2 miles a week and let a lighter week in now and then, the ramp is about six weeks. Six weeks to get there, twelve to hold it, plus the taper. That is a little over four months, and a runner at 12 miles a week gets a longer count and a runner at 28 gets a shorter one.
Your count is yours. Take the week you are in, subtract it from the number, and the gap is your ramp.
If you have been reading about 50Ks for a year and have not signed up, here is the part to hold onto: the count is not a verdict on whether you are ready. It is arithmetic, and you can do it tonight. Our first 50K training guide lays out what those twelve weeks can look like week by week.
A few miles of that ramp will be hard to add without something hurting. If something does, a physiotherapist or sports medicine doctor can tell you what yours is, which is not something a post can do.
Is 8 weeks enough to train for a 50K?¶
It depends on how much of the twelve you have already done without calling it training.
Eight weeks is enough if you are already running close to the race distance each week, and have been for a month or more. In that case you are four weeks into the hold, and the eight left finish it. Think of a runner who has had a steady 25 to 30 mile weekly habit from the winter, and then picks a race eight weeks out.
Eight weeks is a stretch if you are starting from a few runs a week and a long run of ten or twelve miles. You would be ramping and holding in the same eight weeks, and there is no room for a bad week. A bad week is normal. A cold, a work trip, a kid who is sick. The twelve weeks has slack in it for that. Eight weeks from a standing start does not.
The same goes for the searches that say "one month." A month is enough to get a race on your calendar and start the ramp. It is not the whole count for a first 50K unless you are already holding the number.
If the race is eight weeks out and you are not there, you have a few choices. Pick a later race. Pick a different 50K with more room. Or run this 50K at a pace and a walk plan that suits where you are, and plan to finish slowly. All of those are fine. The cutoff, the climb and the night are what you are up against, and they are the same for everyone.
Is six months too long to train for a first ultra?¶
No. Six months is common, and the extra weeks do something useful.
Take the 20 mile a week runner from above. The ramp and the hold add up to about 18 weeks, which leaves roughly eight in six months. Those can go to easy weeks, a race along the way, a trip, a lighter stretch when life gets loud. The twelve-week hold is the part that is not negotiable. Everything before it is flexible, and you get to spend it getting to the number without hurrying.
Where six months goes wrong is when the whole thing is run at the number from week one. Holding 31 miles a week for 26 weeks is a lot to ask of a body that has never done it, and the point of the ramp is that it arrives gradually. Time on feet matters more than speed here: a long slow day counts as a big day. If you are on a trail for four hours at an easy effort, you did the work, whatever the watch says about pace.
Longer than six months is also fine. Nobody is behind. Your earlier weeks are not lesser, they are earlier.
How long does it take to train for a 100 mile race?¶
Longer, and the rule does not carry over cleanly.
Run 100 miles in a week and hold it for twelve weeks, and that is not a plan anyone should follow. My caveat on the rule is that it does not always hold for 100s and longer. For those distances you really should be doing more than just running. That means time on your feet in other ways, back-to-back long days, hiking, strength work, practising food and gear. The weekly number matters less and what you do around it matters more.
For the weeks, published plans are longer. Marathon Handbook's 100 mile plan is six months long, assumes you already have 50K and 50 mile finishes, and describes the whole preparation as often taking two to three years. That is one coach's view, and others will tell you less. The common thread is that a first 100 asks for a base that most first 50K training blocks do not build by themselves.
If you have a 50K behind you and a 100 is where you want to go, the middle step is useful: our post on going from 50K to 50 miles covers what changes after mile 35.
Counting back from your race¶
You do not need a tool for this. Here is the whole method on one page.
- Write down the race distance. That is the number.
- Write down the most you ran in a week over the last month. That is where you are.
- Subtract. Divide the gap by how much you can add each week without something hurting. That is your ramp.
- Add twelve weeks of holding the number. Add the taper.
- Count back from race day. If the date lands in the past, pick a later race, or a shorter one. If it lands with room to spare, keep the room.
If you have been off for a stretch, start step 2 from the running you did when you were last steady, not from the week you wish you had. Credit what you built before. It counts.
NavRun does a version of this when it builds a plan. It reads your last twelve weeks of running, so the plan starts from the weeks you actually ran. For a 50K it builds toward the race distance in a week, with a two-week taper, and for a 100 miler it counts hours instead of miles, which is the caveat above. The 50K plan to just finish shows what that looks like. More on the training plans page.
Your first ultra is not a number of weeks. It is the week you are in, and a date you choose.
Start from what you kept. navrun.app