How Big Should a Calorie Deficit Be? Why Forward Has Three Paces
When you set up Forward, it asks for one decision about speed. Not a slider, not a target date: three paces, called Gentle, Steady and Faster. This post is about the arithmetic behind them and the two places where the app refuses to go further.
From “a kilo” to “a day”
The working rule is that about 7,700 kcal of deficit adds up to roughly 1 kg of body weight. Spread over a week, that turns into a daily number:
| Pace | Per week | Deficit per day |
|---|---|---|
| Gentle | 0.25 kg | ~280 kcal |
| Steady | 0.5 kg | ~550 kcal |
| Faster | 0.75 kg | ~830 kcal |
If you use pounds, the paces are 0.5, 1 and 1.5 lb a week instead, with the same math underneath. We round every deficit to the nearest 10 kcal, because pretending to know your day to the single calorie would be its own kind of dishonesty.
For scale, the NHS suggests that most adults aiming to lose weight cut about 600 kcal a day, for 0.5 to 1 kg a week. Steady sits just under that, and Gentle is there for anyone who would rather barely notice the change.
Then we subtract it from what you burn
A deficit only means something next to what you burn. Forward estimates that in one of two ways:
- With Apple Health: your resting energy plus the active energy your iPhone or Apple Watch recorded.
- Without it: your resting energy from the Mifflin–St Jeor equation, multiplied by 1.2 for a mostly sitting day. That’s deliberately on the low side, so a quiet day doesn’t leave you with more food than you burned.
Burn minus deficit is your daily budget, the number the Today screen counts down from. If you want to see it for yourself, our calorie deficit calculator runs the same math in your browser: enter your details and it shows all three paces side by side.
The first stop: a minimum for every day
Each pace has to clear a floor. Harvard Health’s guidance is that, without a health professional’s supervision, calorie intake should not fall below 1,200 a day for women or 1,500 for men. Forward uses the same two numbers.
If a pace would plan your day below that line, Forward greys it out and won’t let you pick it. For a smaller person who doesn’t burn much, that can rule out all three. We didn’t want the app to simply say no, so in that case Gentle stays available with a smaller deficit: the budget sits at the floor, and the estimated finish date moves later to match. Slower, but still moving.
The second stop: the goal itself
The other limit is on where you’re heading. A goal has to be below your current weight, and it can’t be below a BMI of 18.5 for your height. We wrote about that rule and its limits in why Forward won’t set a goal below a BMI of 18.5.
Why the plan needs a referee
The 7,700 kcal rule is a useful starting point, not a law. As you lose weight, your body gets smaller and burns a little less, so the same deficit produces less loss over time. Kevin Hall’s group at the NIH showed in The Lancet that the real response to a change in intake is slow and curved, not a straight line. The NIH Body Weight Planner is built on that research if you want a more detailed projection.
Forward doesn’t try to model all of that. It keeps the plan simple and lets the scale settle arguments: if your 7-day average isn’t moving after a few weeks at a pace, the estimate was off, and you can switch paces or adjust your numbers. That’s also why the finish date always comes with a tilde.
Sources
- NHS: Obesity treatment
- Harvard Health: Calorie counting made easy
- Mifflin et al., American Journal of Clinical Nutrition (1990): a new predictive equation for resting energy expenditure
- Hall et al., The Lancet (2011): quantification of the effect of energy imbalance on bodyweight
- NIDDK: Body Weight Planner
This article is general information, not medical advice. Talk to a doctor or qualified health professional before changing your diet, exercise or sleep, especially if you are pregnant, have a medical condition or a history of disordered eating. See our health disclaimer.