This book recommends 0.5kg a week in order to avoid muscle wasting, which assumes you are exercising regularly while you lose weight.
0.5kg is also fairly achievable if you don't over indulge on chocolate, crisps or alcohol etc. on a regular basis. It may get tough if you're a social eater or drinker, but as long as your daily calorie intake, averaged across the week, is less than the amount you require then you'll lose weight. A slow steady burn is far easier and a lot more rewarding than losing 1-2kg quickly and bouncing back again.
The 'algorithm' it uses is fairly easy to apply, and has been adapted slightly and used on sites like livestrong. It goes into great details, giving you your daily intake of grammes of fat, carbs and protein.
- Estimate your RMR (resting metabolic rate):
- 31-60 male : (body weight kg x 11.6) + 879
- 31-60 female : (body weight kg x 8.7) + 829
- (There's other age ranges which I'd need to look up again)
- Calculate your daily energy expenditure:
- Sedentary: RMR x 1.4 (n.b. this coefficient assumes some degree of walking during the day)
- Moderate: RMR x 1.7
- Very active: RMR x 2.0
- Estimate the number of calories expended during exercise over the course of a week then divide by 7.
- Add figures from steps 2 + 3
- Reduce your calorie intake by 15%
- Calculate your carbohydrate needs in g - step 5 x 0.6%, divide by 4.
- Calculate your protein needs in g - 1.6g per kg, per day.
- For a percentage, multiply by 4, divide by total calories from step 5, multiply by 100.
- Calculate your fat needs (percentage) : 100 - 60 - (protein %)
- Turn this back into grammes: (cals x fat %) / 9
From my own experience this formula gives you more calorie allowance than you should get on the Sedentary level. If you want to something to calculate it for you, I wrote this calculator based on it.
In my view the livestrong.com version is more refined and a better option.