Dieting Calculator

A lighter body burns fewer calories, so the same food makes a smaller deficit as you go. In the Mifflin–St Jeor formula each kilo lost lowers maintenance by 10 kcal times your activity factor, about 14 kcal a day at light activity. Eating a steady 1,500 kcal, a 70 kg woman of 35 at light activity would take 24.4 weeks to reach 62 kg, not the 21.1 weeks her first day's 418 kcal deficit suggests.

At the weight for which the calories you eat are exactly maintenance. The calculator shows it for a set-amount plan. Nobody needs to get there: once you reach your goal, eat your new maintenance calories (about 1,808 kcal a day at 62 kg in the example) and your weight holds.

If you want to keep the same pace, yes. Choose "Lose at a set rate" and how often to re-adjust: at 0.5 kg a week, re-adjusting every 2 kg, the example goes from 1,367 to 1,340, 1,312 and finally 1,284 kcal a day and reaches the goal in 16.4 weeks. Never re-adjusting is the same as eating a set amount.

Some people plan a week or two at maintenance every few weeks to make a diet easier to keep up. Weight holds during a break, so the plan takes longer by the break weeks before you reach your goal: a week off after every 8 weeks moves the example from 24.4 to 27.4 weeks. Whether breaks help in other ways is still debated.

The calorie deficit calculator tells you how much to eat for a chosen weekly loss today. This dieting calculator follows the plan forward day by day as your weight and maintenance change, so it shows the goal date for a set calorie intake, how the pace slows, where you'd level off, and the calories at each re-adjustment.

It's a model, not a promise. Maintenance comes from a formula, and real bodies also adapt (you may move a little less and burn a little less), so most people lose a bit slower than any simple model. Weigh yourself under the same conditions, look at the trend every 2–3 weeks and adjust by 100–200 kcal if it's off.