London Marathon Training Guide: The Perfect 12-Week Build Up

By Martin Williams — Ex-GB International Marathon Runner, Edinburgh Marathon Winner, 2:17:36 PB

With London Marathon acceptance emails landing and spring marathons on the horizon, panic often sets in. The temptation is to start a gruelling 20-week schedule immediately.

In my experience coaching athletes from beginners to elite, a 16 or 20-week specific build-up is often too long. It leaves you stale, tired, or injured by the time April comes around. My view is simple: the perfect specific marathon block is 12 weeks. But there is a vital catch.

Training to Train

You cannot embark on a 12-week marathon plan from zero. You should start those 12 weeks already in good 10k shape with a solid aerobic base. This makes the 4 weeks BEFORE the plan absolutely key — your "pre-plan" phase. It ensures your body is robust enough to handle the intensity that is coming. Skip this foundation and you risk injury because the jump in load is too high.

The Risk of Peaking Too Early

I often see runners crushing 20-mile runs in January for an April race. They feel invincible in February, but by March they are overcooked. Running a marathon PB is about timing. You want to be on the upward curve as you stand on the start line, not on the way down. A structured 12-week plan concentrates the mind and the body without the mental burnout of a longer block.

The Coach's Outside View

Having a coach is a game-changer compared to a downloaded PDF plan. A good coach works backwards from your goal race date and knows exactly where you need to be 3, 6, and 12 weeks out. More importantly, when life gets in the way — work stress, family illness, travel — a coach can prioritise: skip the easy run, keep the tempo. This flexibility ensures you keep the main thing the main thing.

Targeting London or Manchester? Find out about marathon coaching or read about Lydiard base training principles.