Wondering what your ride really cost you? Your training stress score turns duration and intensity into one number, anchored so that one hour at your threshold equals 100.
This page is part of our guide to training with power.
| Item | Value |
|---|---|
| One hour exactly at FTP | 100 TSS |
| Low-stress single ride | Under 150 TSS |
| Medium-stress single ride | 150-300 TSS |
| High-stress single ride | 300-450 TSS |
| Typical weekly TSS cut to shed fatigue | 40-50% |
The ranges come from BikeTips’ TSS guide. Figures can change and vary by rider, so check the source before you rely on them.
What training stress score measures
Training stress score, or TSS, estimates the physiological stress of a workout by combining how long you rode with how hard you rode relative to your own threshold. A long easy ride and a short brutal one can land on a similar number, which is the point.
The anchor is simple. One hour ridden exactly at your functional threshold power (FTP) scores 100 TSS, and everything else scales from there.
Because TSS is indexed to your threshold, it is personal. A 300 TSS week for a new rider and a 300 TSS week for a Cat 2 racer represent a similar relative stress, even though the absolute watts are very different.
How TSS is calculated
The formula is TSS = (seconds × NP × IF) ÷ (FTP × 3600) × 100. NP is normalized power, a weighted average that reflects how surgy the ride was, and IF is intensity factor, which is NP divided by FTP.
Our page on normalized power explains why NP is used instead of plain average power. For TSS, the key idea is that variable, punchy rides cost more than a steady ride with the same average.
Three inputs drive the result:
- Duration: longer rides add more stress.
- Intensity factor: how hard the ride was relative to your threshold.
- FTP setting: the yardstick for everything else.
Intensity is squared in effect: riding 10% harder adds much more stress than riding 10% longer, according to BikeTips. A long, gentle spin can therefore score less than a short hard session.
BikeTips gives a worked example: a 1-hour ride at IF 0.85, a classic sweet spot session, scores roughly 72 TSS. You never need to compute it by hand, because every major head unit and platform does it automatically.
Still, knowing the formula helps you read the result. If a ride scores higher than you expected, check whether surges pushed the normalized power up, or whether your FTP is set too low.
Why your FTP setting matters
If your threshold setting is months out of date, every number downstream is wrong. Set it too low and every ride looks harder than it was; set it too high and you under-count your load.
Retest or update your FTP whenever your fitness clearly changes. Keep the same FTP setting while it remains representative of your fitness.
Body size is a separate question. TSS is relative to your own threshold, so it does not reward bigger riders; for comparing watts across riders see power to weight ratio cycling.
What the numbers mean for one ride
BikeTips offers rough reference points for a single ride. They are guides, not rules, and your own recovery matters more.
- Under 150 TSS: low stress; most riders recover by the next day.
- 150-300 TSS: medium; some residual fatigue into the following day.
- 300-450 TSS: high; expect leftover fatigue for two days or more.
- 450+ TSS: very high; typically only long, hard days such as a big gran fondo.
Use these to plan the days after a big effort. If a long group ride lands in the high band, make the next day easy rather than stacking another hard session on top.
Using TSS across a week
Adding up daily TSS gives you weekly load, and this feeds the fitness, fatigue and form numbers on a performance management chart. There is no universal weekly target: the right number is whatever your current fitness says you are adapted to, plus a modest overload.
To build, raise the weekly total gradually and watch how you feel. To recover, reducing weekly TSS by 40-50% is usually enough to shed fatigue while keeping the engine warm.
Fitness, fatigue and form from daily TSS
Daily TSS values feed three metrics that together form the performance management chart. Each answers a different question.
- CTL (chronic training load, “fitness”): a weighted average of your daily TSS over roughly the past 42 days.
- ATL (acute training load, “fatigue”): the same calculation over roughly the past 7 days.
- TSB (training stress balance, “form”): yesterday’s CTL minus yesterday’s ATL.
BikeTips describes ATL as the short-term cost you pay for the long-term CTL gain. A rider holding a CTL of 70 is doing about 490 TSS per week.
A negative TSB means you are carrying more fatigue than fitness, which is normal and productive during a training block. A positive TSB means you are fresh.
BikeTips suggests building for two to three weeks, then cutting volume 40-50% for a recovery week so TSB climbs back toward zero. It also advises keeping hard days separated by at least one easy or rest day so ATL never runs away from you mid-week.
Remember what TSS cannot see. It needs measured or estimated power data, usually from a power meter or a smart trainer, and it does not account for sleep, illness, heat or life stress.
Where the term comes from
TSS and IF were created by Dr. Andrew Coggan, and the metrics were later bought by TrainingPeaks and trademarked. Zwift’s “stress points” are really just TSS, the same number you see when you end a ride.
That means you will meet the same idea under different names across apps. The calculation behind it stays the same.
BikeTips lists Garmin, Wahoo, TrainingPeaks, TrainerRoad and intervals.icu among the head units and platforms that calculate it automatically. This site is independent and is not connected to any of them.
Common mistakes when reading TSS
The number is a model, not a measurement of your body. These habits cause most of the confusion:
- Chasing a big number: a high score is not a goal in itself; the right load is the one you can absorb and recover from.
- Ignoring context: the same score feels different when you are tired, ill, hot or short on sleep.
- Comparing with others: your TSS is relative to your own FTP, so a friend’s weekly total says little about what suits you.
- Stale thresholds: an out-of-date FTP distorts every ride, as covered above.
Treat TSS as a log of what you did, then pair it with how you actually feel. When the two disagree, listen to your legs and adjust the plan.
Frequently asked questions
What is a good TSS for one ride?
Show answer
There is no single good number. Under 150 is low stress, 150-300 is medium and 300-450 is high, according to BikeTips’ reference points.
Do I need a power meter to get TSS?
Show answer
Not necessarily. Calculating TSS requires power numbers, so you need measured or estimated power data, usually from a power meter or a smart trainer that reports power.
Is TSS the same as Zwift stress points?
Show answer
Yes. Zwift’s stress points are the same number as TSS.
Why is my TSS wrong?
Show answer
Most often the FTP setting is out of date. Updating an incorrect FTP improves the calculation, but TSS may still differ from how rides feel.
