Twelve weeks to your first triathlon, or your next distance up

In twelve weeks you will go from separate swims, rides and runs to finishing a sprint triathlon. If you already race, the same twelve weeks take you from short-course fitness to a half-distance race day: 1.9 km swim, 90 km ride, 21.1 km run.

Why this works

José Graca finished third of 246 in his age group at the 2026 Ironman World Championship, in 9 hours 20 minutes, on a course in the town where he lives. Nobody starts there. Every long triathlon is built from three ordinary sports, done often, joined together gradually, and tested on a course you can come back to.

The NHS (the UK health service) recommends 75 minutes of vigorous activity a week, or 150 minutes of moderate activity, plus strengthening on at least two days. The CDC, the US public health agency, gives the same weekly figures. The getting-going track below starts at about that amount and stays close to it. The already-fit track goes well beyond it, which is why it builds a little at a time and has easy weeks.

Before you start

Check with your GP (family doctor) if you have a heart condition, high blood pressure, breathing problems, or have not exercised hard for some time.
Pick the race first. Getting going: a sprint or novice triathlon about 12 to 14 weeks away, ideally with a pool swim. Already fit: a half-distance race (1.9 km / 1.2 mile swim, 90 km / 56 mile ride, 21.1 km / 13.1 mile run) at about the same distance in time.
Kit you already have is enough to start: goggles, any working bike with a helmet, running shoes that fit. Get the bike checked over by a bike shop before the long rides.
Learn the swim conditions. If your race is in open water, find a supervised venue (a lido, a lake with lifeguards, a club session) for weeks 6 to 11. Never swim open water alone.
Strength twice a week, 20 to 30 minutes: squats, lunges, step-ups, press-ups against a wall or the floor, and a plank. It counts towards the NHS and CDC strengthening guideline.

The plan

A “brick” is a ride followed straight away by a run. It teaches your legs the change.

Week	Do this	How often	Notes
1–2 (getting going)	Swim 20 min, ride 30 min, run or run-walk 20 min, each on its own day, all at an easy pace.	Each sport once a week, plus strength twice	Easy means you can talk in sentences.
1–2 (already fit)	Swim 2 km, ride 2 hours, run 50 min; plus one session each of 6 × 3 minutes harder on the bike and run.	5–6 sessions a week	Note your time for a steady 1 km swim and a 5 km run as a baseline.
3–4 (getting going)	Swim 25 min (aim for 400 m without stopping), ride 40 min, run 25 min.	Each sport once or twice a week	Rest at the pool wall as often as you need to.
3–4 (already fit)	Long ride 2.5–3 hours; long run 70 min; swim 2.5 km with 10 × 100 m at race effort.	6 sessions a week	Practise eating and drinking on the bike every 20 to 30 minutes.
5	Easy week for both tracks: cut every session by a third.	As before	Recovery is when the training sinks in.
6–8 (getting going)	Add one brick a week: ride 30 min, then run 10 min. Swim 30 min.	4–5 sessions a week	The first minutes of the run feel odd. That is normal and passes.
6–8 (already fit)	Long brick: ride 3–3.5 hours, then run 20–30 min. Long run up to 1 hour 40. Swim 3 km, one session in open water.	6 sessions a week	Ride at a pace you could hold all day.
9	Easy week for both tracks.	As before	Check your race’s start times, cut-offs and kit rules.
10–11 (getting going)	A practice race at home: swim 400 m, ride 20 km, run 5 km, with breaks between if you like.	Once, plus 3 easy sessions	You now know you can cover the distance.
10–11 (already fit)	Race rehearsal: swim 1.9 km, then ride 90 km, then run 30 min, at race pace and with race food.	Once, plus 4 shorter sessions	The rehearsal is the test. Note what you would change.
12	Race week for both tracks: three short, easy sessions early in the week, then rest two days before.	3 times	Lay out your kit the night before. Start slower than you want to.

If it goes wrong

Missed a week: repeat the last week you finished. Do not try to catch up by doubling.
Pain that is sharp, or that gets worse as you go: stop that sport for a few days and keep the other two. If it lasts, see your GP or a physiotherapist.
Always tired: take an easy week early, and check you are eating enough on long days.
Panicky breathing in open water: stop, float on your back with your ears under, and let your breathing settle before swimming on.
Chest pain that spreads or does not ease, severe breathlessness, fainting or signs of a stroke: stop and call 999 (911 in the US).

Track it

One page, four columns: date, sport, minutes or distance, and one line on how it felt. Add the brick sessions in a different colour. Each fortnight, look at the longest swim, ride and run you have done. Those three numbers should rise until week 11.

What next

Go back to the same race next year. Graca races on a course he knows, and the same course and distance give you a time to beat that means something. If you finished a sprint, the next step is an Olympic distance (1.5 km swim, 40 km ride, 10 km run); if you finished a half, the full distance is the long ride and the long run made longer, at the same easy pace. For more on two of the three sports, read our guide to swimming and cycling.

General information, not medical advice. Check with your GP before starting a new exercise programme.