Until you get tested to find your Basal Metabolic Rate (BMR), all those calculators can do is give you an approximation of what you need to eat. The BMR is a measure of how many calories your body burns while you are being a slug on a couch--doing nothing.
The calculators are using a formula that is based on some assumptions on what a typical person your size, height, etc. would have for a BMR. It's usually within a couple hundred calories, but I've had them estimate high.
Measuring the BMR usually involves measuring the air your body breaths while under a level of stress--such as the treadmill machine. Many gyms will offer it as a service, but you might have your doctor figure it out.
After you have the BMR, the rest is easy. If you consume fewer calories than you burn, you'll lose weight. Just a couple words of advice:
- You need a certain amount of protein to protect your muscles--which in turn burn more fat.
- If you need to cut parts of your diet to hit your target calories, don't sacrifice protein. Many women are protein deficient (based on observations from my wellness center)
- You need to burn 3500 calories to lose 1 pound of fat. That also means you need to consume 3500 in excess of your BMR to gain a pound.
- To lose 1 lb per week, you should consume 500 calories less than your BMR.