Fitness challenge not accurately noting miles

Hello wendiwho,

Thanks for choosing the Apple Support Communities. We see your achievements are logging correctly. We have a few steps that may help you resolve this.

We suggest calibrating your Apple Watch to get better measurements and results. Here is how.

Calibrate your Apple Watch for improved Workout and Activity accuracy - Apple Support

"Calibrate your Apple Watch

1. While wearing your Apple Watch, go to a flat, open outdoor area that offers good GPS reception and clear skies.
2. If you have Apple Watch Series 2 or later, you just need your Apple Watch.* If you have Apple Watch Series 1 or earlier, bring your iPhone for GPS. Hold your iPhone in your hand, or wear it on an armband or waistband.
3. Open the Workout app, then tap Outdoor Walk or Outdoor Run. To set a goal before starting, tap .

4. Walk or run at your normal pace for about 20 minutes.

If you don't have time to finish the workout, you can complete 20 minutes over multiple outdoor Workout sessions. If you work out at different speeds, you should also calibrate for 20 minutes at each of the speeds that you walk or run.

Whenever you walk or run outside using the above steps, your Apple Watch continues to calibrate the accelerometer by learning your stride length at different speeds. Calibration can also improve the accuracy of your calorie calculations in the Workout app, and the calorie, distance, Move, and Exercise calculations in the Activity app. 

Improve your Workout and Activity accuracy

Your personal information, such as your height, weight, gender, and age, is one of the things your Apple Watch uses to calculate how many calories you burn and more. Learn how to update your personal information."

We hope this helps.

Cheers!