Calculate your cycling Training Stress Score (TSS) from power, FTP, and ride time, or find the ride time and power you need to hit a target TSS.
Cycling Training Stress Score (TSS) Formula
TSS = (t * NP * IF) / (FTP * 3600) * 100
IF = NP / FTP
- TSS is the Training Stress Score for the ride (unitless)
- t is the ride duration in seconds
- NP is the Normalized Power for the ride in watts
- IF is the Intensity Factor, your Normalized Power divided by your FTP
- FTP is your Functional Threshold Power in watts, the highest power you can sustain for about an hour
Because IF equals NP divided by FTP, the formula simplifies to a version that is easier to work with when planning rides:
TSS = hours * IF^2 * 100
The calculator uses these formulas in three directions. In the default mode it takes your ride time, power (Normalized Power, average power, or an effort level if you do not have a power meter), and FTP, then returns TSS along with your Intensity Factor and TSS per hour. The ride time mode rearranges the simplified formula to hours = TSS / (IF^2 * 100), which tells you how long you need to ride at a given intensity to reach a target TSS. The power mode solves for the Normalized Power you would need to hold, using NP = FTP * sqrt(TSS / (100 * hours)).
By definition, riding at exactly your FTP for one hour produces a TSS of 100. Every score is anchored to your own threshold, so a 100 TSS ride represents a similar physiological load for a beginner and a professional.
TSS Earned Per Hour at Different Intensities
Because TSS scales with the square of the Intensity Factor, small changes in intensity have a large effect on how quickly training stress accumulates. This table shows the TSS you earn per hour at common intensities and how long you would need to ride to accumulate 100 TSS at each one.
| Intensity Factor (IF) | Typical effort | TSS per hour | Time to earn 100 TSS |
|---|---|---|---|
| 0.55 | Recovery spin | 30 | 3 h 18 min |
| 0.65 | Easy endurance | 42 | 2 h 22 min |
| 0.75 | Tempo | 56 | 1 h 47 min |
| 0.85 | Sweet spot | 72 | 1 h 23 min |
| 0.95 | Threshold intervals | 90 | 1 h 6 min |
| 1.00 | FTP effort | 100 | 1 h 0 min |
| 1.05 | Short race or hard intervals | 110 | 54 min |
Once you know the score for a single ride, this second table helps you judge how much recovery it will likely demand before you can train with quality again.
| Single ride TSS | Training load | Expected recovery |
|---|---|---|
| Under 150 | Low | Generally recovered by the next day |
| 150 to 300 | Medium | Some residual fatigue the next day, gone by day two |
| 300 to 450 | High | Residual fatigue for about two days |
| Over 450 | Very high | Fatigue lasting several days; plan easy days after |
Example Problems
Example 1: TSS for a completed ride. You rode for 1 hour 30 minutes with a Normalized Power of 210 W, and your FTP is 250 W. First find the Intensity Factor: IF = 210 / 250 = 0.84. Then apply the simplified formula: TSS = 1.5 * 0.84^2 * 100 = 1.5 * 0.7056 * 100 = 105.8. The ride scores about 105.8 TSS, a solid sweet spot session that should leave only mild fatigue the next day.
Example 2: Ride time for a target TSS. You want a 200 TSS endurance day at an easy pace of IF 0.65. Rearranging the formula: hours = 200 / (0.65^2 * 100) = 200 / 42.25 = 4.73 hours, or about 4 hours 44 minutes. To bank the same 200 TSS at tempo (IF 0.75), you would only need 200 / 56.25 = 3.56 hours, about 3 hours 33 minutes.
Frequently Asked Questions
Can you calculate TSS without a power meter? Yes, approximately. The calculator includes an effort-level option that assigns a typical Intensity Factor to how the ride felt, from a recovery spin (IF around 0.55) to an all-out race (IF around 1.02), and applies the same formula. This estimate usually lands within 10 to 15 percent of a power-based score. Heart-rate-based alternatives (hrTSS) work on the same principle. Once you own a power meter, power-based TSS is more reliable because it does not drift with heat, caffeine, or fatigue the way heart rate does.
How much TSS should you accumulate per week? As a rough guide, recreational riders typically handle 200 to 350 TSS per week, competitive amateurs 400 to 600, serious racers 600 to 900, and professionals 800 or more. More important than the absolute number is the trend: avoid increasing weekly TSS by more than about 5 to 7 percent from one week to the next, and cut volume by 30 to 40 percent every third or fourth week to absorb the training.
Why does this TSS differ slightly from TrainingPeaks or my head unit? Training platforms compute Normalized Power from your second-by-second power file using a 30-second rolling average raised to the fourth power, then averaged. When you type in a single NP value here, small rounding differences are normal. If you enter average power instead of Normalized Power, the result will read low on variable rides, because surges raise NP above average power. For steady indoor trainer sessions the two are nearly identical.
