Accuracy of zFTP

How accurate is the zFTP? I am waiting until the weekend to do a ramp test to determine my FTP, but while looking around on my Zwift account found it has an estimated FTP based, I believe, on how I’ve been riding so far. I will update this thread with what I find, but am curious what others have found. Thank you.

zFTP is not your FTP. You shouldn’t expect them to match.

Yes, it was explained to Zwift that this would confuse users.

No, they didn’t listen.


Maybe not, however when expanding the “More info” section, the description provided by Zwift is:

Estimate of your current Functional Threshold Power (FTP), the power you can sustain for a long period of time, i.e. > 40 min.

So it’s not “traditional” FTP as in 95% of a 20 minute test for example, but Zwift still want to describe it as FTP.

I think it’s both confusing and acceptable.

As Iñigo San-Millán might ask, “FTP for how long?” * As it is, FTP is an estimation; and at least Zwift don’t describe this in terms of a 60 minute duration.

Although zFTP is not your FTP (even as calculated by Zwift), it should be roughly in the ball park I think.

e.g. for my recent numbers (in the past few days):

224W 20 minutes
213W FTP (as calculated by Zwift, 95% of 224)
220W zFTP

More to the point for @1760Ghost the zFTP will be based on the efforts you’ve done in the past 60 days. If none of them have been hard or sustained, it won’t mean much for now. The same panel that shows your zFTP should show your best 20 minute power as well; multiple that by 0.95 to get your more traditional FTP estimation - but that assume the 20 minutes were all out.

* okay find your FTP again we’re talking about FTP for what? For 10 minutes for 50 minutes for 40 minutes and then have a formula a percentage or… FTP is - I’m not saying that it is the same thing as 220 minus your age to establish your maximum heart rate which we know that is has never been proven proven and it doesn’t work, but it’s a surrogate or a proxy that um in in some cases might work in some other cases might not work

from this GCN video:


Thank you Daren.

The ramp test is not a good FTP test.

I’d recommend the 20 minute test or even the long 1 hour test for most accurate results.

The ramp test is more like a MAP test and the FTP is calculated from it.

Ad a newbie I would start with a ramp test to see where I’m roughly at and then (after a rest) I would do the 20 minute test and pace it based on the FTP from the ramp test.

Accurate for 60 minutes perhaps if you can actually sustain that effort and are absolutely depleted at the end. :smiley:

For beginners in particular, pacing a 60 minute test or even a 20 minute test is difficult. Very difficult perhaps.

I think the benefit if the ramp test is that it’s easier to pace as that’s done for you. And it’s over sooner so people are more likely to regularly test.

The main thing is to use the same test consistently. Don’t do a ramp test and then try and benchmark improvements by doing a subsequent 20 minute test for example.


A quick internet search came up up with this article on this topic:

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Hi Neal, our Fitness Metrics FAQ has some good info on zFTP.

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it should but i think it varies on what your short term power is also as
zFTP - 297w
20 minute - 285w so around 271w eFTP - 271w

vast difference in my numbers after doing a 12min effort

I don’t trust zFTP in the least nor the fact that they haven’t explained how they calculate it


zFTP prior to Ramp Test was 205. The Ramp FTP conclusion was 226. Do what you will with that info.