Keep Fit by Numbers

As usual during the winter, my weight has gradually been creeping up. In fact it seems I've put on nearly half a stone. (Counting in kilos may make it sound less, but doesn't make it any less bulky, I'm afraid, so I'll stick to what I'm used to.) So I've decided to join a keep-fit class. I was pleased to hear that doing an hour's physical exercise three times a week increases your life expectancy, but then I started to do some calculations:

At just over forty, I may expect to live another 30 years. That's 1560 weeks of keep-fit class. The class itself is an hour, but I need to allow 15 minutes for changing and showering, and 10 minutes each way to get there and back. Let's say a total of 4 hours 45 minutes a week. Over thirty years that adds up to 7410 hours dedicated to exercise etc.

If I'm adding a year to my life by doing this, that's 8760 hours. Even if we think of it as a retirement year during which I have no other commitments, I can expect to spend around 2920 hours sleeping and 1095 eating, cooking and cleaning (at a conservative estimate of 3 hours per day for meals and housework). Nor must we forget the 247 exercise-associated hours of that extra year.

I seem to end up with a net loss of 282 hours or nearly twelve whole days. I'm beginning to wonder if it's really worth it?