Free tool
When should I start marathon training?
Put in your race date. Get the day to start, your four phases, when the longest run falls, where a tune-up race fits, when to taper — and which weeks Christmas and New Year land in.
Pick your race date to see your dates.
How the dates are worked out
A marathon plan is built backwards from race day, not forwards from whenever you start. The taper comes first — the final three weeks, cutting volume progressively so you arrive fresh. The longest run sits immediately before it, about three weeks out. Everything earlier is split between base, build and peak in proportion, with a lighter cut-back week every fourth week so the body absorbs the work.
That ordering matters. Plans built forwards tend to run out of weeks at the end, which is how people end up squeezing the taper or doing their longest run a fortnight before the race. The spring marathon guide covers the reasoning, and the evidence on tapering covers the last three weeks.
Questions
How many weeks before a marathon should I start? Most plans run 16 to 20 weeks. Sixteen suits someone already running comfortably three or four times a week; eighteen to twenty gives a newer or returning runner room for a slower build and the odd bad week.
When should my longest run be? About three weeks out, just before the taper. Many plans peak around 30–32 km (18–20 miles). You do not need to run the full distance in training.
When do I start tapering? Two to three weeks out, cutting volume progressively while keeping some race-pace work.
When should I run a tune-up half? Around five to six weeks before the marathon.
A planning aid, not coaching or medical advice. If you are new to running, returning from injury or have a health condition, talk to a professional before starting a marathon build.