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Fitness-Fatigue Form (TSB) Calculator

Enter your CTL (fitness) and ATL (fatigue) to see your current form and freshness.

How it is calculated

You supply two numbers that your training software has already calculated: CTL (the long-term, "fitness" load) and ATL (the short-term, "fatigue" load). The tool does not compute them from workouts. It only takes the difference:

form (TSB) = CTL − ATL

The result is labelled by fixed bands, following Andrew Coggan's approximate guides: above +10 is Fresh, from −10 up to +10 inclusive is Neutral, and below −10 is Fatigued. Values are shown to one decimal. Both inputs must be zero or higher; the result can be negative. The labels depend only on the number, so they cannot know whether you are in a build phase, where a negative form is expected, or a taper.

Worked example

Your training platform shows CTL 55 and ATL 72. The form is 55 − 72 = -17.0. Because that is lower than −10, the tool labels you Fatigued. Had the numbers been CTL 62 and ATL 71, the form would be −9.0, which is inside the Neutral band, and at CTL 72 and ATL 60 the form of 12.0 would read as Fresh (exactly 10.0 is still Neutral).

Try this example →

Common mistakes

  • Entering CTL and ATL the wrong way round. Fitness goes in the CTL box; swapping them flips the sign, so a tired athlete looks fresh.
  • Using daily training stress or one workout's score in place of CTL and ATL. The two inputs are rolling averages, not a single day.
  • Reading a negative form as something to fix at once. Heavy blocks normally sit well below zero; the label only describes the number, it gives no advice.
  • Comparing forms from different platforms. Each uses its own scale for training stress, so only compare CTL, ATL and form from the same source.
  • Using a form value at today's number to predict race day. Form changes daily, so enter the values you expect on the day of the event, not those from the heaviest week.

Sources

About this calculator

The Banister impulse-response model splits an athlete's training load into two competing effects: CTL (Chronic Training Load, often called “fitness”), a long, roughly 42-day exponentially weighted average of daily training stress, and ATL (Acute Training Load, “fatigue”), a short, roughly 7-day exponentially weighted average of the same stress. Subtracting the two, TSB = CTL − ATL, gives Training Stress Balance, commonly just called “form.”

A strongly negative TSB means recent training has outpaced adaptation and the athlete is carrying heavy fatigue, while a positive TSB signals freshness — often engineered deliberately in the taper before a race. This framework, popularized by platforms like TrainingPeaks, underlies periodization planning for cyclists, runners, and other endurance athletes.

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