Power-Duration Assessment:

Critical Power Calculator

Understand your performance beyond FTP

Most cyclists are familiar with FTP — but it only tells part of the story.

Critical Power (CP) gives a clearer picture of what you can sustainably produce and how much work you can do above that level before fatigue takes over. This matters when pacing, training decisions, and repeated hard efforts actually count.

Think of it like a battery

Your performance can be thought of as two parts:

• Critical Power (CP) — the power you can sustain for longer periods without rapidly fatiguing

• W′ (W prime) — your finite battery for work done above CP

When you ride above CP, you draw down the battery.

When you ride below CP, it gradually recharges.

Two riders can have the same FTP but very different batteries and fatigue behaviour — which is why real-world performance often doesn’t match expectations.

What this calculator does

This calculator estimates your Critical Power and W′ using three key efforts that most cyclists already have in their data:

• Peak 5-second power

• Maximal 3-minute effort

• Maximal 12-minute effort

Together, these capture neuromuscular peak power, high-intensity capacity, and sustained aerobic performance. It’s a practical, repeatable way to understand how you actually perform — without complex lab testing.

How to get useful results

These efforts can come from a structured testing session or sessions, races, or hard/intentional training intervals.

For the most meaningful results:

• be reasonably well-rested

• use a reliable power source

• pace the 3- and 12-minute efforts evenly

• avoid sprinting early and fading

• allow good recovery if efforts are done in one session (approx 30 minutes+)

This doesn’t need to be perfect — it just needs to reflect genuine maximal efforts.

What this helps you understand

CP and W′ help answer questions like:

• why you fade late in hard efforts

• why repeated surges feel disproportionately costly

• why training looks right on paper but falls apart in practice

This isn’t about chasing numbers — it’s about making better decisions.

A note on interpretation

Critical Power isn’t a fixed value. It becomes more useful as good data accumulates over time. This calculator provides a clear starting point — a more informative framework than relying on FTP alone.

If your results raise questions about pacing, training structure, or recovery between hard efforts, coaching support can help turn this information into better decisions. Are you more of an anaerobic punchy rider able to accelerate up those steeper hills, or are you more of an aerobic engine who struggles to match the surges but can power on?