I think it will also depend which stroke you are doing and how fast you go. Most people do a leisurely breast stroke when you want to be doing a reasonably fast front crawl. But exercise is part of a healthy lifestyle so do it for this reason and because you enjoy it rather because you're looking for a big loss.
I've lifted this info on the calories burned while swimming, which may be helpful
How many calories are used whilst swimming?
There are many factors that contribute to the number of calories you burn whilst swimming, these include.
- your weight
- distance swum
- time spent swimming
- stroke used to swim
To keep it simple here is an estimate and a formula that will help you work out how many calories you are likely to have used during your swim.
Leisure swim (not laps)
3.2 calories per stone per 5 minutes
Breaststroke (moderate intensity)
5.3 calories per stone per 5 minutes
Water aerobics (moderate intensity)
2.2 calories per stone per 5 minutes
for example if you weigh ten stone and swim leisurely for 30 minutes you are likely to have burned 192 calories.
If you swim faster than what could be described as moderate then you can increase the amount of calories burnt.