Weight Loss Calculator – Calorie Deficit and Goal Date
Work out how many calories to eat to reach a goal weight, and about how long it will take. The plan stays within the 1 to 2 lb a week range recommended by the CDC and NHS, never drops below a calorie floor, and recalculates your needs as you get lighter.
Weight loss calculator
How to use the weight loss calculator (calorie deficit)
- Enter your details. Add sex, age, current weight, height and a typical activity level. These set your maintenance calories with the Mifflin-St Jeor equation.
- Set a realistic goal weight. Pick a goal that keeps your BMI at 18.5 or above. The tool rejects goals below that, and goals that are not lower than your current weight.
- Choose a pace. Gentle is about 0.5 lb a week, steady about 1 lb, and the fastest option about 2 lb. Slower paces are easier to sustain.
- Read the plan. See daily calories, the deficit, the starting loss rate, the estimated time and goal date, and your projected weight after 12 weeks.
- Review every month. Weigh weekly, compare with the 12-week projection and re-enter your new weight every 4 to 8 weeks, since lower weight lowers maintenance.
Not medical advice. This calculator gives general information from published formulas and is not a diagnosis, treatment or substitute for a doctor, midwife or registered dietitian. Check with a doctor first if you take medicine, have a medical condition, are pregnant or breastfeeding, or have ever had an eating disorder.
How the plan is built
Maintenance = BMR × activity factor
Daily calories = maintenance − (pace in lb/week × 500), never below the floor
Weekly change = daily deficit × 7 ÷ 7,716 kcal per kg
Each week the tool lowers your weight, recalculates your BMR at the new weight and keeps your daily calories fixed. As maintenance falls, the deficit narrows and progress slows, which is why the estimate is longer than the simple rule.
Worked examples
A 40-year-old woman, 90 kg to 70 kg, 1.65 m, lightly active, steady pace. Maintenance is about 2,160; eating 1,660 gives a 500 deficit and about 0.5 kg a week at first. The simple rule says 40 weeks for 20 kg; the weekly recalculation says about 65 weeks.
A 45-year-old man, 230 lb to 190 lb, 5 ft 10 in, sedentary. Maintenance 2,320, eat 1,820, about 1 lb a week at first, and roughly 53 weeks for 40 lb. After 12 weeks the projection is about 219 lb.
A gentle 0.5 lb pace from 90 kg toward 70 kg. Intake of 1,910 holds a 250 deficit at first, but maintenance falls to meet it. The tool reports that weight levels off short of the goal rather than promising a date.
Safe-limit rules in this tool
The pace never exceeds 2 lb (1 kg) a week. Intake never drops below 1,200 (women) or 1,500 (men). Goals under BMI 18.5 are rejected. If your maintenance is already near the floor, the tool refuses to cut further and points you to a clinician. Use the BMI calculator to see where a goal sits.
Making the number work
Pair the calories with protein and fibre using the macro calculator, add daily movement with the steps calculator, and estimate workout burn with the calories burned calculator. The CDC also lists sleep, stress management and support as part of a healthy plan, and suggests asking a health care provider about referral to a registered dietitian or clinical programme.
Frequently asked questions
How fast should I lose weight?
The CDC says people who lose weight gradually, about 1 to 2 pounds a week, are more likely to keep it off. The NHS gives the same 1 to 2 lb (0.5 to 1 kg) a week. This calculator does not offer a faster pace.
Why does the time estimate differ from the simple 3,500-calorie rule?
The simple rule keeps your deficit fixed. In reality maintenance drops as you lose weight, shrinking the deficit. This tool recalculates maintenance every week, which is closer to the dynamic model of Hall and colleagues (2011).
What if the calculator says my goal is not reached?
At a gentle deficit your maintenance can fall to your intake before you reach the goal, so weight levels off. Choose a slightly faster pace, increase activity, or revisit the goal with a dietitian.
Why is there a calorie floor?
The tool does not go below 1,200 calories for women or 1,500 for men. NHLBI starting ranges are 1,000 to 1,200 for most women and 1,200 to 1,600 for most men, and anything lower is a very low calorie diet that the NHS says needs specialist support.
How much weight loss improves health?
The CDC says even modest loss helps: 5% of body weight, for example 10 lb for someone weighing 200 lb, can improve blood pressure, cholesterol and blood sugar. The NHS says 5 to 10% can improve health.
Can I use this to gain weight or during pregnancy?
No. The goal must be below your current weight, and the tool is not for pregnancy, breastfeeding, under 18s or anyone with an eating disorder. Use the calorie calculator for gain, and ask your midwife or doctor in pregnancy.
Do I need to exercise as well?
It helps. The NHS suggests 45 to 60 minutes of activity most days for weight loss, and the CDC recommends at least 150 minutes of moderate activity a week for adults. Even walking counts toward both.
Related calculators
Calorie Calculator (BMR & TDEE)
BMR, TDEE and maintenance calories with the Mifflin-St Jeor equation.
Macro Calculator
Daily calories and grams of carbs, protein and fat for your goal.
BMI Calculator
BMI, category and healthy weight range for adults.
Steps to Miles Calculator
Convert steps to miles or km and back, using your height.
Sources and references
- CDC – Steps for losing weight (about 1 to 2 pounds a week)
- NHS – Overweight and obesity in adults (BMI thresholds, waist-to-height, 1–2 lb a week)
- Hall KD et al. (2011) – Quantification of the effect of energy imbalance on bodyweight, Lancet
- NIDDK – Body Weight Planner (dynamic weight-change model)
- NHLBI – Facts About Healthy Weight (calorie ranges for weight loss)
- Mifflin MD et al. (1990) – A new predictive equation for resting energy expenditure in healthy individuals, Am J Clin Nutr
- CDC – Adult activity: an overview (150 minutes a week of moderate activity plus muscle strengthening)
About this calculator
Written and maintained by Rashid Mehmood, founder of CalcTen. The formulas are unit-tested against hand-worked examples, and the content is reviewed whenever product sizes or guidance change. Last updated 14 November 2026. See our editorial policy.
This calculator gives general information and is not medical advice, diagnosis or treatment. Results are estimates based on population averages. Talk to a doctor or other qualified health professional about your own situation. Read the disclaimer.