It's often said within my circle of running friends: "If it's not on Strava, it never happened." Now Strava has released a blog that explains something they have dubbed the 'Strava tax'.

Don't worry, the Chancellor hasn't found a way of filling a fiscal black hole via your running efforts – although 20% VAT on kit does a pretty good job of that already – the 'Strava tax' is that frustrating phenomena experienced when you upload a run, say 5.00kms, from another source and Strava records and displays it as 4.99kms – a 'tax' of 0.01km deducted from your hard work in training!

Why does this sometimes happen? Strava admits its policy of rounding down data it receives to ensure accuracy, authenticity and consistency is responsible, and it has no intention of changing any time soon.

runABC reported on the fractional inaccuracies of GPS watches in this 2023 article. Strava explains that although your watch may display an even number, such as 10kms, particularly after you have jogged a few extra metres to round it up, what is actually recorded and shared with Strava is perhaps 9.993kms, and Strava rounds this down to 9.99kms – close, but no cigar!

This is common across the board, with different brands of wearable tech using slightly different methods to calculate and display data, known in the tech world as a 'parser'. Strava uses a common parser to calculate and display all activity, irrespective of the nuances caused by various brands using bespoke parsers for their devices (which partly explains the post-race huddle to discuss slight inconsistencies between Garmin, COROS, Suunto, etc.).

Strava says: "When Strava started in the early 2010s, GPS wasn’t as good as today. It often overestimated distance, especially on straight roads with slight GPS drift. To stay honest to the effort, we made a call starting in 2012: always round down. We adopted the same principle we apply to racing: if you’re running a 5K and your watch says 5.00km before the finish line, you don’t stop running – you finish. So we applied that logic to how distances were displayed. It’s a conservative approach but one that matches the seriousness with which we view the data athletes trust us to handle."

In the blog, Strava explains why it intends to continue to round down data. The main reason is that adding a factor to smooth out and effectively round up the data would create even more inaccuracy, and each small discrepancy would be magnified thousands of times across the 120 million Strava users in over 190 countries, undermining Strava's claims:

"Strava’s role in the fitness ecosystem is bigger than just showing you a nice round number on your phone. Strava is the ledger of record for human activities – a responsibility we take seriously. We’re the place where the effort gets documented, the work gets acknowledged, and the numbers carry weight, whether it’s for your own personal progress, a weekly challenge, or a world-record attempt."

It seems there is no escape from death, taxes, Strava tax or running circles round the car park to 'top up' at the end of training runs!

Photo courtesy of Maarten van den Heuvel on Unsplash