Functional threshold power (FTP) is the highest power output you can sustain for roughly one hour on the bike. Most cyclists never actually ride a full 60-minute all-out effort to find it. Instead, they use shorter test protocols and apply a percentage-based formula to estimate the number. The three most common methods are a 20-minute test, an 8-minute test, and a ramp test, each with trade-offs in accuracy, difficulty, and accessibility.
What FTP Actually Represents
FTP marks the boundary between exercise intensities you can hold in a steady state and those you can’t. Below your FTP, your body can clear metabolic byproducts roughly as fast as it produces them. Above it, fatigue accumulates rapidly and you’ll be forced to slow down within minutes. The practical value of knowing this number is that it anchors your training zones, letting you target specific energy systems during workouts rather than guessing based on how hard something feels.
You’ll sometimes see FTP compared to a related concept called critical power (CP). Both describe a threshold between sustainable and unsustainable effort, but they’re measured differently and don’t always produce the same number. CP is derived from multiple exhaustive efforts lasting 2 to 15 minutes, then calculated with a mathematical model. Research published in the International Journal of Exercise Science found that CP was significantly higher than FTP in highly trained cyclists, meaning they aren’t interchangeable. For most recreational and competitive cyclists, FTP is the more widely used and practically useful metric.
Equipment You Need
You need a device that measures power in watts. The two main options are a dedicated power meter (typically built into your pedals, crank arms, or rear hub) or a smart trainer that calculates power internally. Either works, but consistency matters more than absolute accuracy. A good pedal-based power meter is accurate to about 2%, and most smart trainers fall in a similar range when properly calibrated.
Before every test, calibrate your equipment. For a smart trainer, that means running a spindown calibration where the flywheel spins freely and the software adjusts for resistance changes caused by temperature. For pedal or crank-based power meters, perform a zero-offset (sometimes called a “zero reset”) through your head unit. If you test indoors, use the same fan setup and tire pressure each time. Small environmental differences, especially heat buildup indoors without adequate cooling, can meaningfully reduce your power output and give you a falsely low result.
The 20-Minute Test
This is the most widely used FTP test. You ride as hard as you can sustain for 20 minutes, record your average power, then multiply by 0.95. That 5% reduction accounts for the difference between a 20-minute effort and the theoretical 60-minute effort FTP is meant to represent.
Start with a thorough warm-up of at least 15 to 20 minutes. Include some progressive efforts building from easy spinning up to near-threshold intensity, plus a few short bursts to open your legs. Many protocols also include a 5-minute all-out effort before the main test, followed by 5 to 10 minutes of easy spinning. This “blowout” effort pre-fatigues your anaerobic system so the 20-minute result better reflects your aerobic threshold rather than being inflated by a hard early surge.
The biggest mistake in a 20-minute test is starting too hard. If you go out at a pace you can’t hold, the last 10 minutes become a survival exercise and your average power drops well below what a more even effort would have produced. Aim to ride the first 5 minutes at a pace that feels hard but controlled, then gradually increase through the middle portion. The final 3 to 5 minutes should feel like everything you have left. If you finished with energy to spare, your number is too low. If you blew up at minute 12, it’s unreliable.
For example, if your average power over 20 minutes was 260 watts, your estimated FTP would be 260 × 0.95 = 247 watts.
The 8-Minute Test
The 8-minute protocol is a good option if you’re newer to structured training or find the mental challenge of a 20-minute effort too daunting to pace well. Instead of one long effort, you perform two 8-minute all-out intervals with about 10 minutes of easy recovery between them. Your FTP is calculated by averaging the power from both intervals and multiplying by 0.90.
The two-effort structure helps with pacing. If you go too hard in the first interval, you get a second chance to dial it in, and the formula averages both. The 10% reduction (compared to 5% for the 20-minute test) accounts for the shorter duration allowing higher power output. This test is slightly less precise than the 20-minute version because the gap between 8 minutes and 60 minutes requires a larger correction factor, but it’s a practical trade-off for riders who would produce unreliable 20-minute results due to pacing errors.
The Ramp Test
Ramp tests have become the default in most indoor training apps because they’re short, require no pacing skill, and are highly repeatable. After a warm-up, you start at 100 watts and the resistance increases by 20 watts every minute. You simply keep pedaling until you physically can’t maintain the required power or cadence. The whole effort typically lasts 10 to 20 minutes depending on your fitness.
The app then calculates your FTP using an algorithm based on the power output of your final completed stage and how long you lasted in the stage where you failed. You don’t need to do any math yourself. The trade-off is that ramp tests favor riders with strong anaerobic capacity, who can push through the final high-power stages longer than their aerobic fitness alone would support. If you’re a diesel-type rider who excels at steady efforts but fades quickly above threshold, a ramp test may slightly overestimate your FTP. If you suspect this, validate your ramp test result with a 20-minute test or by checking whether you can complete threshold workouts at the prescribed intensity.
How to Use Your FTP Number
Once you have an FTP value, it defines seven training zones based on percentage ranges developed by exercise physiologist Andrew Coggan:
- Zone 1, Active Recovery: below 55% of FTP
- Zone 2, Endurance: 56 to 75%
- Zone 3, Tempo: 76 to 90%
- Zone 4, Lactate Threshold: 91 to 105%
- Zone 5, VO2 Max: 106 to 120%
- Zone 6, Anaerobic Capacity: above 121%
- Zone 7, Neuromuscular Power: short maximal sprints, not percentage-based
If your FTP is 247 watts, your endurance zone runs from about 138 to 185 watts, and your threshold zone sits between 225 and 259 watts. These ranges let you follow training plans with precision rather than relying on perceived effort alone. When a workout prescribes “3 × 10 minutes at threshold,” you know exactly what wattage to hold.
When and How Often to Retest
Retest your FTP roughly every 30 days. That’s frequent enough to capture fitness gains from a training block without testing so often that it disrupts your training schedule. If your training zones start feeling too easy (threshold intervals feel like tempo) or too hard (you can’t complete prescribed workouts), those are signs your FTP has shifted and a retest is overdue.
Use the same test protocol each time so your results are comparable. Switching between a ramp test and a 20-minute test will introduce variation that has nothing to do with your fitness. Test on the same equipment, in the same environment, at a similar time of day, and after a similar amount of rest. One or two easy days before a test is enough for most riders. Treat the test like a race effort: go in rested, fueled, and hydrated, with your legs feeling fresh rather than carrying fatigue from a hard training week.
Choosing the Right Test for You
If you’re new to power-based training, start with the ramp test. It requires zero pacing strategy, finishes quickly, and gives you a working number to build from. As you gain experience with how threshold efforts feel, graduate to the 20-minute test for a more accurate picture of your sustainable power. The 8-minute test sits in between, offering a good balance for riders who want more accuracy than a ramp test but aren’t confident pacing a full 20-minute effort.
No single test is perfectly accurate. FTP is an estimate by definition, since almost nobody actually rides a true 60-minute time trial to validate it. What matters most is consistency in how you test, so that changes in your number over time reflect real changes in fitness rather than differences in protocol, equipment, or conditions.