Your spring marathon starts on 20 December, whether you have noticed or not

Here is a piece of arithmetic that catches people out every single year.

• NN Marathon Rotterdam — Sunday 11 April 2027. A sixteen-week block starts Sunday 20 December 2026.
• Haspa Marathon Hamburg — Sunday 25 April 2027. Sixteen weeks back is Sunday 3 January 2027.

If you have entered a fast European spring marathon, your training does not begin in February when the weather turns. It begins in the week of Christmas, and its hardest phase runs through January.

Why this is the awkward part of the year

The mid-block weeks — roughly weeks four to ten — are where a marathon is actually made. They are also, in Northern Europe, weeks that land in January and early February.

That means the highest-volume, highest-quality period of your year coincides exactly with the period when it is dark at four, wet most days, and icy on the mornings it is not. The sessions that matter most are scheduled into the conditions that make sessions hardest to do.

This is not a motivation problem and treating it as one is why people fail it. It is a logistics problem with a predictable shape, and it can be planned for in September rather than fought in January.

Plan the block around the constraint

Know which sessions are non-negotiable. In a sixteen-week build, usually two a week: one quality session and the long run. Everything else can move, shorten, or become easy running without much cost. Protect those two absolutely and the block survives a bad month.

Decide the wet-and-dark alternative now, in advance, while it is still September and the decision is cheap. The runners who get through a European January are not tougher. They decided in autumn what happens when the weather says no, so that in January there is no decision left to make — just a session to do.

Count backwards and put it in a calendar. 20 December for Rotterdam. 3 January for Hamburg. Twelve-week builds start 17 January and 31 January respectively, if that suits you better.

The thing worth being honest about

Running outside is better. That is why we do it, and on a cold bright January morning there is nothing else like it.

But a marathon block is sixteen weeks long, and in this part of the world perhaps a third of those sessions will fall on days when going outside is unpleasant, unsafe, or simply not going to happen after the day you have had. Losing that third is the difference between a spring personal best and another year of wondering.

The weather gets a vote. It does not get a veto.