Interesting calculations...

simonb mentioned the following site, http://www.bodybuilding.com/fun/calrmr.htm and I thought I'd have a go and a look at the results. This is based on a fat percentage of 45%, which is roughly what my scales say I am (they're funky ones which measure resistance by passing current through your feet). Anyway, this is their conclusion:

( before )

Which is not that far from what fitday reckons is my Basal Metabolic Rate of 1784 really. Fitday reckon I use another 775 cals just living, based on a lifestyle of desk work. Simon recommends multiplying RMR by 1.4 for a lightly active lifestyle. Both these come out at around 2600 cals a day.

If I put in my target weight (11 stone, around 70kg) and the percentage of fat that would be given the same lean mass (23%) then I get the following result instead:

( after )

Mulitply that by 1.4 and I should be on around 2100 cals a day at that point. Which I guess makes sense, as I'll still be somewhat bigger (and hence using more cals) than the average woman of food packaging.