The fitbit app currently calculates "% of your goal" for the swimming stats incorrectly. For instance, my daily goal is 5 miles (= 8800 yards). When I swim 2900 yards, I SHOULD get 33% of my goal, but instead I get 20% of my goal, implying my daily goal is ~8.24 miles. I believe the app is converting the distance in yards to distance in miles by dividing by 1800 yards/mile instead of 1760 yards/mile and also converting the "to goal distance" from miles to km (multiplying by 1.609 km/mi), but keeping the units in miles.
Correct method: 2900 yards / (5 miles * 1760 yards/mile) = 32.95%
Current method: 2900 yards / (5 miles * 1.609 * 1800 yards/mile) = 20.03%
This problem seems very similar to the Android problem (ca 3/2020 - 10/2023) where a daily goal of 5 miles was showing 5 miles as only ~5/8 complete. (Probably converting the 5 miles to 8.047 km but keeping the units as miles.)
