Safe-rate guidance reflects widely published public-health ranges
How big a deficit is reasonable
A calorie deficit just means eating less than you burn. The question that matters is how big a gap to run. Public health sources generally describe about half a pound to two pounds a week as a workable, sustainable range for most adults; going faster than that tends to cost muscle along with fat and is harder to keep up. The mild and standard loss options on this page sit inside that range. The aggressive setting does not exist on this tool for a reason: any plan cutting harder than roughly 1,000 calories a day is something to plan with a doctor or registered dietitian, not a webpage.
The math, step by step
Weight is estimated with the Mifflin-St Jeor equation (1990), the same BMR formula used on the BMR calculator on this site. That resting number is then scaled by your activity level to get maintenance calories, which is the "eat this much and your weight should stay roughly flat" figure. From there, the tool subtracts 250 calories a day for the mild option and 500 for the standard loss option, based on the long-standing rough estimate that a pound of fat corresponds to about 3,500 stored calories. The gain option adds 500 calories a day for anyone building muscle or trying to put on size.
None of these subtraction amounts are ever allowed to push the target below your own BMR, since eating under that line for long stretches is not something this calculator is built to recommend.
Why we don't chase a single perfect number
Body weight moves for reasons that have nothing to do with fat loss: sodium intake, hydration, hormones, even how much you ate the night before a weigh-in. A single day's number on the scale is close to useless on its own. What actually tracks a deficit is the trend across several weeks. If the scale isn't moving the way this page predicts after three or four weeks of consistent eating, that is useful information, and worth adjusting the target for, not a sign the math is broken.
Other tools worth a look
- TDEE Calculator, for the maintenance number on its own
- Macro Calculator, to split a calorie target into protein, carbs and fat
- Ideal Weight Calculator, for a healthy-range reference point
FAQs
What counts as a safe rate of weight loss?
Public health guidance generally points to about 0.5 to 2 pounds a week for most adults, which lines up with the mild and moderate options here rather than the more aggressive one.
Why does the calculator stop the deficit from going below BMR?
Eating consistently under your resting energy need is generally something people only attempt under medical supervision. The floor keeps the tool's suggestions inside a range that fits normal, unsupervised use.
Will I actually lose exactly what this predicts?
No. Real weight loss is noisy week to week because of water retention, hormones and measurement error. The number here is a planning estimate over a period of weeks, not a guarantee for any single day.
Should I eat back the calories I burn exercising?
The activity-level dropdown already accounts for regular exercise, so most people do not need to add exercise calories on top. Doing both usually erases the deficit the calculator set up.