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Race Power Calculator

How do I get an accurate race prediction using Stryd's race power calculator? Why is my race power calculator wrong?

Updated over a week ago

Stryd Race Calculations Definition

Stryd uses data from your last 90 days of training to estimate different race predictions. By combining the user's personal fatigue factor and their Power-Duration Curve, a model can predict how they might perform in a race in ideal circumstances (a flat course, with the same environmental conditions that the user trains with). The prediction will be based on how quickly they become fatigued and how their power output decreases over time.

Details on the features that contribute to the Stryd Race Predictions are as follows:

  1. Fatigue Factor: When you exercise, your body uses energy, and as you continue to exert yourself, you become tired, or "fatigued." The fatigue factor is a measure of how quickly you tire out. A higher fatigue factor means you get tired faster.

  1. Power-Duration Curve (PDC): This is a graph that shows the relationship between the power (energy) you can exert and how long you can maintain that exertion. Imagine sprinting versus jogging. You can sprint at full speed for a short time, but you can jog at a slower pace for a much longer time. If you plot your maximum power at different time lengths (for example, 1 minute, 5 minutes, 10 minutes, etc.), you will get a curve that generally goes down as time increases. This is the Power-Duration Curve. The "slope" of this curve essentially describes how quickly your power decreases as time goes on.

In simpler terms, think of running a race like driving a car with a certain amount of gas. The fatigue factor is how quickly your car uses gas, and the Power-Duration Curve is how fast you can drive at different gas levels. Given the ideal circumstances, you can predict how far and how fast the car (or runner) can go before it runs out of gas (or gets too tired to continue at the same speed).

Account Requirements for Accurate Race Predictions

Your running data from the last 90 days needs to meet the following requirements:

You must have:

  1. A valid racecourse uploaded via PowerCenter

  2. At least 1 workout conducted around your Critical Power

  3. At least 1 workout conducted around the intensity for your target race distance

  4. An accurate Model Curve on your Power Duration Curve that extends from the 10-minute duration to the 20-minute duration.

    1. Note: This means that you must have a well-balanced Power Duration Curve and max efforts around the 10 to 20-minute duration. For example, a max effort in the 7-minute duration would be effective in modeling your 10-minute duration and a 25-minute activity would be effective in modeling your 20-minute duration. Alternatively, a max effort in the 15-minute range may also effectively model your capability from the 10 to 20-minute duration.

  5. Have an accurate Critical Power

    1. Note: If you use auto-calculated Critical Power, your auto-calculated Critical Power likely will be accurate if you meet requirement #3 by having a maximum effort near the 10-minute duration and the 20-minute duration.

Race Calculator in the Stryd app

Currently, the Race Calculator on the Stryd app only shows race estimates for the mile, 5k, 10k, Half Marathon, and Marathon race distances. If you have another race distance that you would like to see an estimate for, you will need to check PowerCenter Race Power Calculator. Please note that the PowerCenter Race Power Calculator is a membership-only feature.

Race Calculator in PowerCenter

Stryd's Race Power Calculator is intended to help you set an achievable target power or target time and to see what the possible outcome might be as your race day approaches. Stryd’s Race Power Calculator uses your previous 90 days running activity to recommend a ‘Target Power’ or ‘Target Time’ for both generic flat courses and real courses (from an uploaded course profile).

To access the Race Power Calculator:

  1. Log in to your PowerCenter account at

  2. Tap the Tools icon on the left side of your PowerCenter

  3. Input the distance of your upcoming Race

  4. Tap Calculate

Upload Course to Race Power Calculator

You can upload .fit and .GPX files to the Race power calculator for the most accurate race time prediction from Stryd. GPX files must include timestamps so cannot be pulled directly from online mapping tools like Google Maps or MapMyRun, but some GPX files can be uploaded to Garmin Connect which will add a timestamp. Downloading the file from Garmin Connect after uploading can give a valid file for Race Power Calculator upload. Here is how to upload your race course:

  1. Log into Stryd Powercenter.

  2. Navigate to the Race Power Calculator tab on the left side of the screen.

  3. Select "Select Course" in the upper right.

  4. In the dropdown menu, select "Upload Course"

  5. Select "Select File" and add the .fit or .gpx file to the account.

Deleting a Race Course:

You can delete a race course by going to your PowerCenter account and:

  1. Choosing the 'Settings' tab on the left side of the screen

  2. On the top of 'Settings' select 'Courses'

  3. Finding the course you'd like to delete from the list and select the three-dot menu

  4. Select 'Delete'

Race Power Calculator: Not Enough Data

Stryd's Race Power Calculator uses your past 90 days of running activity to estimate your recommended target power to race at. In some conditions, you may not have enough data:

Invalid CP. In this case, you have not generated a Critical Power yet. Read more on Critical Power to better understand how we determine your CP and how to keep it up-to-date.

Not Enough Data. In this case, you need more runs to calculate a race prediction. Stryd needs at least five runs to do so, though more runs, with a lot of variety and with a similar course profile, will yield the most accurate results. In addition to having completed 5 runs, the Stryd platform analyzes your data on a fixed schedule. It can a few extra days after completing your 5th run before you can use the Race Power Calculator.

Estimated Power Target based on 10k race power

The Race Power Calculator (Stryd Membership feature) and the Race Calculations are the best tools to know your race power and times. However, you can estimate your power target based on your CP manually as well:

Distance (km)

% 10k power

















Your event might be a different distance between 10k and 42.2k, and you can estimate your power for your event with the following formula (does not work for distances less than 10k):

% 10k power = -0.325 * race distance (km) + 103.25

This is a simple linear estimation and is not fully accurate.

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