People at swimming try to burn off fat. If you think your belly or bum is fat try doing Dolphin kick using your whole body to burn off fat and get muscle. If you are a girl try not to get abs cause people would think your a freak on the beach. I am guessing that around an hour in the pool. Do a warmup, main, and cooldown so you wont puke or have major cramps.

Well, presuming that you are using swimming as a device to get back into shape, I would break up your routine a tad more. Firstly, as I believe someone else already said, you need to add a little variety to your strokes, having a defined warm-up, main set, and maybe a little bit of cool-down. Secondly, to burn fat, you should be getting your heart rate up, the basis of all good cardio. Breast stroke is the calmest of the four traditionally practiced strokes, which will not burn as much fat as say, freestyle. Thirdly, push yourself and commit to a timetable, a timetable will enhance your swimming experience enourmously, because you will be able to keep exact track of the time and distance you have done in a day. Culminating these three things you should have an hour long set that looks something like this:

–Warm-up–
2 x 100 freestyle on 2:00 apiece
2 x 50 Backstroke on 55 seconds
2 x 50 Breaststroke on 1:05 apiece (could be a push, but you’ve been doing quite a bit of breaststroke, so you should be able to go through these quickly)
2 x 25 Butterfly sprint on 1:00 (so you have plenty of rest. If you can’t do Butterfly, do free in this until you can)

Rest for 2:00

–Main Set–
4 x 100 freestyle on 2:00
Rest 1:00
1 x 200 IM (individual medley; 50 of each stroke) 5:00 (should give you some rest)
3 x 100 freestyle on 2:00
Rest 1:00
2 x 200 IM on 5:00
2 x 100 freestyle on 2:00
Rest 1:00
2 x 150 Breaststroke on 3:00
150 Freestyle on 2:00 (really fast part to cap off the workout)

– Cool-down –
Just swim a few laps at an easy pace to cool off and let your heartbeat slow down.

The marked time of the workout takes 55 minutes, providing you five for cool down and whatever. Note, I am not a swim coach by any means, but I do know a little bit about swimming from swimming year round, and will be going into my sophomore year of high school as a varsity swimmer, swimming varsity last year as well. My average swim practice usually spans between 2 and 2 and a half hours and 3.5 to 5 miles. I wish you luck in your veture here to stay in shape Hope this helped!