How to use the Critical Power calculator

Follow this step-by-step guide to calculate your Critical Power (CP) and W′ using the Critical Power calculator after completing your testing. You will also learn how to generate your SEMIPRO Power training zones and enter them into TrainingPeaks.

Before you start

You need two recent max efforts: one in the 3–5 minute range, and one in the 12–20 minute range. The 1-day test protocol is in every SEMIPRO plan. If you have not tested yet, do the protocol first — these efforts feed the calculator.

Step 1 — Open the calculator

Go to semiprocycling.com/critical-power-calculator. You will see two input fields: time and average power, one for each effort.

Step 2 — Enter your numbers

Enter the duration and average power of each effort. The calculator returns your Critical Power (CP) in watts and your W′ (W prime) in kilojoules. These two numbers define almost everything about how you train.

Step 3 — Get your SEMIPRO Power zones

The calculator outputs your SEMIPRO Power zones based on your CP:

• Recovery · 40–54% of CP — light aerobic, effortless
• Endurance · 55–74% of CP — steady, conversational
• Tempo · 75–89% of CP — moderate, just below threshold
• Threshold · 90–105% of CP — hard sustained

Step 4 — Enter them in TrainingPeaks

In TrainingPeaks, open Settings → Zones → Power. Select SEMIPRO Power as the zone scheme (or create a custom zone set named that way) and enter each zone's wattage range from the calculator output. Save.

When to retest

Every 6–8 weeks of consistent training, or any time sessions feel meaningfully easier or harder than the prescribed effort. Retesting too often leads to noisy numbers; not often enough leaves you riding with stale targets.