race prediction inacurate, slower than already recorded trainings

Yeah my 5k on garmin is predicted to be 25:42 whereas it says my best 5k with the watch is 20:42 which was during a 6k. Before I had the watch, during a 5.5 my 5k was sub 20. Adding on that much time is kinda crazy. Maybe it’s because I haven’t had the watch long, but still kinda crazy. 

Although most online feedback suggests that only training results and VO2Max are used in the algorithm that Garmin uses, I think resting heart rate / stress levels are taken into account as well: after every intense traning session, even when my VO2Max has improved, my race predictions are more pessimistic/slower. Yet, after a longer rest (e.g. 2 or 3 days of rest or easy cross training instead of 1) my predictions get very optimistic. I feel like the more pessimistic predictions are also the case after a few walking or cycling activities that I did not record: my Garmin does recognize the activities, but still registers the stress levels during those activities (which it does not do with the activities you actively select on your watch). 

Also seeing this for forerunner 255. Have had the watch for 4 months. The race predictor had my marathon at 3:22, and I just finished an actual marathon with 3:10.

My times are actually far more off, and it's crazy. I ran a continuous 5k yesterday at a 19:09. My mile time is 5:35. My real 10K time is in the 41's. Yet is has my race predictions at...5K - 21:00, 10K 44:00, and so on. It is literally minutes off the 5K I just did yesterday, would love for Garmin engineers to explain that to me. I also just did a 10K race a few weeks ago minutes better than it is predicting. It is so far off it messes with my head and I am about to switch watches. It does the same for my fiancee and her times, way slower than she has recently done in races.

Yeah same. Did a 19:02 in autumn and still said 21 to 22 range. This confuses me because over the course of a few weeks that time I did a couple 5k races, all low 19 range and the watch still stuck with its 20-21 something. I too would love to hear from the garmin engineers 

I actually reached out to support and they replied to tell me that it takes a while for my watch to get to know me.  Every week, the predicted times get a bit closer to what I know I can actually do (and what I have actually done while wearing this exact watch!) but they are still very far off.  But at this point, I've still only had the watch for five weeks, so I'm still giving it the benefit of the doubt.

I have had my Fenix 6 since December of '21, so length of time wearing it is not the problem. lol. It should know me by now and know my times are way faster than their predictions. I read it's because it's based solely off VO2 Max. Well, if that's the case, then something is still off either way, whether it's the VO2 Max or whatever. It should be a relatively quick programming thing, I would think, to have the watch recognize when you just ran a time well faster than the predictions.

Totally agree with this. I have talked with customer support and they gave me total BS as to why it's not working correctly. 'wear your watch more' it's on my wrist literally 24-7 not sure how that's going to change much. 

I was worried too about my ox readings and about a month ago I went to the doctor and her ox monitor read 98% which my Garmin regularly read low 90s and living at 8000' of elevation and growing up at or below sea level I would like to know how I'm progressing but yeah it's not accurate at all. 

I am wondering whether you have found a solition yet. I have my fenix7 for over a year now and race predictor has worked adequatly this whole time until my last race in january. Since then it has gone up, up, up and claims my 5k in 30mins. Super annoying.