Interesting calculations...

[lnr]

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:

Your Estimated Resting Metabolic Rate

Your Weight: 220 Pounds or 100 Kilograms.

There are five different methods that are commonly used to calculate your RMR. All methods are used here and then averaged. Descriptions of the methods used are down below.

According To Calculation Method One*

Your RMR is 1763 Calories per day.

According To Method Two*

Your RMR is 1774 Calories per day.

According To Method Three*

Your RMR is 1764 Calories per day.

According To Method Four*

Your RMR is 2195 Calories per day.

According To Method Five*

R is 1712 Calories per day.

Your RMR Average From All Methods

Your Average RMR is 1842 Calories per day.

How This Calculator Works

Method One Description:

Males: 66+ (6.22 x weight (lbs)) + (12.7 x height (inches)) - (6.8 x age)
Females: 655 + (4.36 x weight (lbs)) + (4.32 x height (inches)) - (4.7 x age)

Method Two Description: Harris-Benedict Equations

BW = body weight in kilograms, HT = height in cm, Age in years
Men: RMR = 66.473 + (13.751*BW) + (5.0033*HT) - (6.755*Age)
Women: RMR = 655.0955 + (9.463*BW) + (1.8496*HT) - (4.6756*Age)

Method Three Description: REVISED Harris-Benedict Equations

BW = body weight in kilograms, HT = height in cm, Age in years
Men: RMR = 88.362 + (13.397*BW) + (4.799*HT) - (5.677*Age)
Women: RMR = 447.593 + (9.247*BW) + (3.098*HT) - (4.330*Age)

Method Four Description: Quick Estimate Formula

Men: BW (in kg) * 24.2
Women: BW (in kg) * 22.0

Method Five Description: Fat Free Mass Formula

This is the same for men and women.
RMR = 1.3 * Fat Free Mass (in kg) * 24

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:

Your Weight: 154 Pounds or 70 Kilograms.

There are five different methods that are commonly used to calculate your RMR. All methods are used here and then averaged. Descriptions of the methods used are down below.

According To Calculation Method One*

Your RMR is 1475 Calories per day.

According To Method Two*

Your RMR is 1491 Calories per day.

According To Method Three*

Your RMR is 1487 Calories per day.

According To Method Four*

Your RMR is 1537 Calories per day.

According To Method Five*

Your RMR is 1678 Calories per day.

Your RMR Average From All Methods

Your Average RMR is 1534 Calories per day. 

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.