The 20-minute power-based field test is the simplest, most reliable way to find your Functional Threshold Power (FTP) and set your training zones. It's free, repeatable, and tells you something a lab test can't: are you actually getting faster on the bike? Below is the FasCat protocol — the same one we've used with thousands of athletes since 2002 — including the FTP math, a repeatability checklist, and an indoor alternative.
Listen: The 20-Minute Field Test Podcast
Frank walks through the protocol, the math, and the most common mistakes athletes make on the FasCat Podcast:
Why a 20-Minute Field Test?
In a former life I conducted hundreds of experiments as a research scientist in biotechnology and academic medical research labs — spinal cord research, cancer, novel cancer therapies. At FasCat, we still run "experiments" on our athletes' physiology, just on the bike instead of in a lab. The most practical, most relevant test of cycling fitness — short of a 40k time trial — is a 20-minute power-based field test.
We've done lab-based MLSS tests in the past, but cyclists need to retest two to three times per year, and the lab is cost-prohibitive for most athletes. A properly conducted field test cuts to the core of cycling performance and gives a great physiological assessment of the athlete[1] — making it indispensable for our coaches and the self-coached athlete alike.
How to Do a 20-Minute FTP Field Test
The protocol is simple: ride as hard as you can for exactly 20 minutes. Just like a 20-minute time trial. Record your average power output and use that number both as a benchmark and to calculate your wattage-based zones (see the FTP math below).
Pick the Right Road
Whenever possible, choose a steady 2–3% grade hill free of stop signs, descents, and any section of road that forces you to stop pedalling. A 20-minute climb like this Strava segment is ideal. Steeper climbs bog down most athletes' cadence and skew the result. Some athletes make more power uphill than they do on the flats; some are the opposite. Pick what works for you — and then commit to it. Apples to apples.
If your terrain doesn't offer a long climb, that's fine. Find a stretch of road where you can ride flat-out for 20 minutes uninterrupted. Pay extra attention to wind and humidity, since both move your aerodynamic drag around. As long as you return to the same piece of road, start from the same spot, and run the same warm-up under similar conditions, your test will be repeatable.
An all-out 20-minute effort elicits the physiological response that's been shown to be "the single greatest determinant of cycling performance in mass-start events"[1]. We've experimented with full 60-minute field tests, and honestly very few athletes can sustain that focus for an hour. When they can, it's a mental match we'd rather not burn.
FTP Math: Average Power → FTP
Take your average 20-minute power and subtract 5–10% to arrive at your one-hour FTP:
- Subtract 5% for slow-twitch, aerobic athletes.
- Subtract 10% for athletes with a well-developed anaerobic system (sprinters, criterium racers).
- Subtract 7.5% if you don't know your athlete's anaerobic capacity.
Example: 320 W average × 0.925 = 296 W FTP.
Repeatability: The Whole Point
Find a stretch of road free of stop signs, intersections, and corners — anything that would slow you down. Then go as hard as you can. Don't hold back. The catch: remember everything about this test and duplicate it next time.
Repeatability checklist
- Powermeter: Same one, calibrated. Different powermeters produce different numbers.
- Bike: Same bike, same weight (including bottles), same body position, same tires and tire pressure.
- Kit: Same jersey, shorts, helmet — your aerodynamic profile should match test to test.
- Wind & weather: Test on a windless day with similar humidity. Air density matters.
- Temperature: Avoid testing in temperature extremes that don't match your previous test.
- Freshness: Show up rested, fueled, hydrated, and motivated. You have to go full gas.
- Warm-up: Run the exact same warm-up before every field test.
Controlling every variable except your fitness is what lets you and your coach interpret the result honestly. The details look picky, but they're what make the comparison meaningful.
Test, Train, Retest
If you have a new powermeter or are starting a training program, do a baseline field test for two reasons:
- To set your wattage-based training zones.
- To establish a benchmark for measuring future improvement.
Then train for 6–8 weeks and retest under the same rested conditions on the same road. If your average power went up, your training is working — keep going. If it stayed flat or dropped, something needs to change. It really is that simple.
Many of our six-week training plans begin and end with a field test for exactly this reason — so you can see the gain in black and white.
How Often Should You Test?
We recommend 2–3 field tests per year — typically at the start of each major training block. Beyond that, the test costs more than it gives back. Log every test in your training diary along with the conditions, the road, the warm-up, and how you felt. That history is what lets you and your coach plan a winning season.
Regular testing is the best way to track real performance, which is why we don't rely on mean-maximal, mFTP, or power-profile estimates that filter out everything except your hardest efforts. The 20-minute test also gives you data you can compare directly to race efforts — TT segments, breakaways, and long climbs.
Indoor 20-Minute Field Test
Indoor power tends to be slightly lower than outdoor power because of cooling and motivation. Always compare indoor results to indoor results and outdoor to outdoor — never mix the two. For a trainer-specific protocol, see our indoor field test guide.
Field Test vs. Auto-FTP Detection
If you're a CoachCat athlete, the App's auto-FTP detection updates your FTP from your ride data in the background, every week. Most CoachCat athletes never schedule a formal test — and that's by design. The field test is still useful as a benchmark workout and as a hard data point at the start and end of a block, but you don't have to plan your training around it.
Summary
- Ride as hard as you can for the full 20 minutes.
- Upload your data and record the average power.
- Subtract 5–10% to estimate your FTP and set zones.
- Make the test 100% repeatable — same road, same kit, same conditions.
- Retest in 6–8 weeks to confirm the training is working.
- For indoors, follow our indoor field test guide.
Testing yourself is a great start — but the ultimate measure of performance is performance itself. Sign up for a race, go hard, and duke it out.
Frequently Asked Questions
How do I calculate FTP from a 20-minute field test?
Take your average power for the 20-minute effort and subtract 5–10% to estimate your one-hour Functional Threshold Power. Use 5% for slow-twitch aerobic athletes, 10% for athletes with a well-developed anaerobic system, and 7.5% if you don't know the athlete's anaerobic capacity.
How often should I do a 20-minute FTP field test?
Two to three times per year. Test at the start of a training block and again 6–8 weeks later to measure whether the training is working. More than three tests per year burns mental matches without adding useful data.
What kind of road or hill should I use?
Ideally a 2–3% steady-grade hill free of stop signs, descents, and any section that forces you to stop pedalling. Steeper climbs bog cadence down and skew results. If you don't have a climb, use a flat stretch of road and return to the exact same spot under the same conditions for repeatability.
Why a 20-minute test instead of 60 minutes?
Most athletes can't sustain the mental focus required for a true 60-minute all-out effort, and when they can, it burns a mental match we'd rather save for a key race. The 20-minute test elicits the same physiological response that's been shown to be the single greatest determinant of cycling performance in mass-start events.
Can I do the 20-minute field test indoors?
Yes — but indoor power tends to be slightly lower than outdoor power. Compare indoor tests to indoor and outdoor to outdoor; never mix the two. See our indoor field test guide for the trainer-specific protocol.
Do I still need to do a field test if I use CoachCat?
Not on a schedule. CoachCat's auto-FTP detection updates your FTP in the background from your ride data, so most CoachCat athletes don't need formal tests. A field test is still useful as a benchmark workout and as a hard data point at the start and end of a training block.
Reference
[1] E.F. Coyle, A.R. Coggan, M.K. Hopper and T.J. Walters. "Determinants of endurance in well-trained cyclists." Journal of Applied Physiology 64:2622–2630, 1988.
For further reading, see our companion guides on FTP testing, FTP vs. Critical Power, and auto-FTP detection in CoachCat.
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