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How the calorie deficit calculator works
- Your maintenance calories. The calculator estimates your BMR with the Mifflin-St Jeor equation and multiplies it by your activity factor, exactly like the TDEE calculator.
- Your goal. If your goal weight is below your current weight, it plans a deficit. If it’s above, it plans a surplus.
- Your pace. Each kilogram of body weight is treated as about 7,700 kcal, so the daily deficit is your weekly pace × 7,700 ÷ 7. At 0.5 kg a week that’s about 550 kcal a day; at 1 lb a week, about 500.
- Safety limits. The pace is capped at 1% of your body weight per week and flagged above 0.75%. Your target never drops below 1,200 kcal for women, 1,500 kcal for men or 1,350 kcal for “other”, in line with the reduced-calorie ranges in the 2013 AHA/ACC/TOS obesity guideline. Targets are rounded to the nearest 10 kcal.
- Your goal date. The date comes from the distance to your goal divided by the pace you’ll really get once the limits are applied.
Why the limits matter
A faster plan can look appealing on paper, but very large deficits are hard to stick to and leave little room for protein, fiber and the foods you enjoy. The CDC notes that people who lose weight at a gradual, steady pace of about 1 to 2 pounds a week are more likely to keep it off than people who lose it quickly.
Here’s what the limits look like for a 25-year-old woman who is 165 cm, 60 kg and sedentary, and who asks for 1 kg a week:
| Step | Result |
|---|---|
| Maintenance (TDEE) | 1,345 × 1.2 ≈ 1,614 kcal |
| Requested pace | 1.0 kg a week |
| Pace cap (1% of 60 kg) | 0.6 kg a week, flagged as above 0.75% |
| Target before the minimum | 1,614 − 660 ≈ 954 kcal |
| Minimum for women | 1,200 kcal |
| Final target | 1,200 kcal a day |
| Real pace | (1,614 − 1,200) × 7 ÷ 7,700 ≈ 0.38 kg a week |
Rather than promise a date that the plan can’t deliver, the calculator recomputes it from the deficit that’s left after the minimum. In this example, reaching 55 kg would take about 93 days instead of the 35 the original request implied.
Why the goal date is only a guide
The 7,700 kcal per kilogram figure is a useful rule of thumb, but bodies aren’t static. As you lose weight, your energy needs fall, so the same intake produces a smaller deficit. Modelling research in The Lancet found that the body’s weight response to a change in intake is slow, with a half-time of about a year, and that people with more body fat can expect a larger loss for the same change in intake.
That’s why this calculator shows a straight-line estimate and labels it as one. If you want to see how adaptation might change your timeline, the NIH’s Body Weight Planner models it in detail.
No deficits for teens
This calculator is for adults. The Calorix app never sets a calorie deficit for anyone under 18, because teens need energy to grow; it keeps them at a maintenance target instead. If you’re worried about a teen’s weight, talk to their pediatrician.
Making a deficit easier to live with
- Keep protein up. A higher protein target helps you feel full and protects lean mass. See the protein calculator.
- Watch the trend, not the day. Daily weight swings with water and salt. Look at the weekly average.
- Log the easy-to-miss calories. Cooking oil, dressings and drinks add up. Our guide to logging restaurant meals covers the usual suspects.
- Expect plateaus. If the trend stalls for three weeks or more, review your logging first, then adjust your target by 100 to 200 kcal.
How Calorix uses this
During setup, Calorix asks for your goal weight and lets you pick a pace on a slider while the projected date updates live, with the same cap and floor as this page. After that, your weigh-ins build a smoothed weight trend, and the projected goal date updates from your real progress instead of a straight line. Toasty, your ember companion, cheers on the habit and never comments on your body.
For a full breakdown of how the numbers are built, read how Calorix calculates your calorie target.
Updated October 9, 2026
