Calculation of the ETA

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Markus Burkhardt

• April 14, 2025 09:52

I have a question about the data field ‘ETA’.

I love this function, I used it for trail running on my Garmin Fenix 3 over 10 years ago.

The time that is displayed is unfortunately not quite realistic at the beginning. I know it takes a while for a system to display a target time, but after 10 km it should be the case.

Funnily enough, the finish time was only relatively correct with a deviation of +/- 5 minutes after the first climb of about 3 kilometres, but by then I was already running 15 kilometres.

Before that, the planned finish time was at a pace of I would roughly say 23-25 KM/h purely mathematically. The funny thing is that my average speed after 10 kilometres was around 21-22 km/h.

So how is the ETA calculated?

Maybe Hammerhead can say something about this?

 

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  Markus Burkhardt

  • April 20, 2025 14:46

  Never an answer?

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  Bhagyashree

  • April 21, 2025 17:24

  Hi Markus, Just to explain how it works: during the first hour of the ride, we use a weighted average of your current speed and 15 MPH. After that, it switches to a weighted average of your speed over the last hour and your total ride average. That’s why the ETA might not feel realistic early on, but usually gets more accurate as the ride goes on. Our team plans to improve this calculation in future updates to make it even more reliable. Thanks again for your feedback.

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  Markus Burkhardt

  • June 22, 2025 13:44

  Can you improve the feature? It is absolutely useless in the first 90 mins.

  Why don't you use the average speed?

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  Udo Marx

  • June 25, 2025 22:25
  • Edited

  @Bhagyashree:

  Thanks for explaining how the ETA is calculated.

  A start calculation with 15 mph, regardless of bike/route type and ascent/descent seems not very sophisticated. And 15 mph are to much for me (old man on MTB rides through forrest and trails).

  If you would use the average speed of the latest rides or a setup parameter instead it would become more realistic, especially for me, I'm usually doing round trips with similar elevation profile.

  I would like to use the ETA for a decision whether I can do a route in time e.g. before a date or before sunset. Therefore I need a reasonable ETA at route start. With the current 15 mph start calculation, the result is far off and useless for me.

  For long term, you should develop a ETA calculation, which considers the bike type (MTB, gravel, race), the route type (trail, road) and the elevation profile and personal fitness.

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