How many people finish a marathon worldwide each year?

How to get close to this number

Count the races. There are a few thousand marathons worldwide each year, with the largest drawing tens of thousands of finishers and most drawing a few hundred. A handful of giant events plus a long tail of small ones produces a total around a million.

The trend in the explanation is the genuinely interesting one and it runs opposite to expectation: average finishing times have got slower over the decades. That is not a decline in fitness — it is a change in who runs. The field shifted from competitive club athletes to ordinary people raising money and ticking off a goal, which lowers the average while raising participation.

That inversion is a general pattern worth recognising. Whenever an activity broadens from specialists to the general public, its average performance falls even as its total output rises, and a statistic that looks like decline is actually a statistic about access. The same applies to chess ratings, exam results and amateur music.