Weight loss goal date calculator

How the date is worked out

The calculator assumes a steady pace: the weight between you and your goal, divided by how much you lose or gain each week. Choose a target date instead and it works the other way, giving the weekly pace that date would take. The milestones sit on the same straight line, so halfway is the day you'd be half the distance to your goal.

It's the sum Weight Loss Tracking Buddy does when you set a goal. The app also works out a daily calorie budget from your height, age and how active you are, and that budget never goes below 1,200 kcal. When a fast pace would take it lower, the app moves your date later rather than promise one the budget can't reach. The calorie deficit calculator shows that too.

Why real progress isn't a straight line

Your weight goes up and down from one day to the next with water, salt and whatever's still in your gut, so a single weigh-in says little about your progress. And as you get lighter you use a little less energy each day, so the same budget moves you a little more slowly than it did at the start. Researchers who modelled this found the old rule of thumb, 3,500 kcal for every pound, overstates how much you lose over the long run (Hall and colleagues, 2011).

So treat the date as a guide rather than a promise, and judge your progress by your trend over a few weeks. That's what the weight charts in the app are for, and why your weight changes every day explains the ups and downs.

Choosing a pace

Most people do best losing 1 to 2 lbs (0.5 to 1 kg) a week, which is why the calculator, like the app, warns you past 2 lbs a week. A slower pace means a later date, but one you're more likely to reach and stay at. If you're pregnant or breastfeeding, under 18, have had an eating disorder or have a medical condition, talk to a doctor before setting a goal.

Sources

• Hall KD, Sacks G, Chandramohan D, et al. Quantification of the effect of energy imbalance on bodyweight. The Lancet, 2011; 378(9793): 826 to 837.
• NHS, Managing your weight.