acalculator

What is my weight loss timeline?

Enter your body details, goal weight and the calories you plan to eat each day. See how many weeks it takes and the date you reach your goal.

Your numbers

Units
Sex
Multiplies your BMR by 1.2, 1.375, 1.55, 1.725 or 1.9.
More options
BMR formula
You reach your goal on
January 26, 2027

Eating 1,600 calories a day, you reach your goal weight in about 17 weeks, on January 26, 2027.

Weeks to your goal
17
Days to your goal
119
Calories you burn now (TDEE)
1,927
Daily deficit now
327
Calories you burn at your goal weight
1,864
Loss in the first week
0.6 lb
Weeks by the 3,500-calorie rule
15.3

Answer for the example date Tuesday, September 29, 2026. It changes to today's date when the page loads.

You reach your goal on: January 26, 2027. Eating 1,600 calories a day, you reach your goal weight in about 17 weeks, on January 26, 2027.

Weeks to your goal by calories you eat a day

This calculator gives general information only. It is not medical advice and does not replace a doctor or other health care provider. Talk with a professional about your results. Terms of use

How to calculate

Estimates how long it takes to reach a goal weight eating a fixed number of calories a day, with daily energy needs (Mifflin-St Jeor or Harris-Benedict × activity) falling as weight falls.

Example with the default inputs (Sex Female, Age 30, Height 5 ft 5 in, Weight 150 lb, Activity Light: exercise 1 to 3 days, Goal weight 140 lb, Calories you eat a day 1,600, Start date September 29, 2026, BMR formula Mifflin-St Jeor) on the example date Tuesday, September 29, 2026: Eating 1,600 calories a day, you reach your goal weight in about 17 weeks, on January 26, 2027.

Method: Days to goal = (7,716.2 ÷ s) × ln(D₀ ÷ D_g), where D₀ and D_g are the daily deficits (TDEE − intake) at the current and goal weights and s is the fall in TDEE per kilogram (activity factor × BMR weight coefficient).

  • A pound of body weight is 3,500 calories (7,716.2 calories a kilogram).
  • Daily needs are the BMR (Mifflin-St Jeor or revised Harris-Benedict) × the activity factor, recomputed continuously as weight falls; age, height and activity stay as entered.
  • The daily intake stays the same until the goal. The goal date rounds the days up to a whole day.
  • Other changes the body makes during a diet are left out, so real loss is often slower still.
  • This is an estimate for planning, not medical advice.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. Sex Female, Age 30, Height 5 ft 5 in, Weight 150 lb, Activity Light: exercise 1 to 3 days, BMR formula Mifflin-St Jeor, Goal weight 140 lb, Calories you eat a day 1,500, Start date 2026-10-01 gives Calories you burn now (TDEE) 1,926.737388, Daily deficit now 426.737388, Calories you burn at your goal weight 1,864.368437, Weeks to your goal 12.666821, Days to your goal 89, You reach your goal on 2026-12-29, Loss in the first week 0.8 lb, Weeks by the 3,500-calorie rule 11.716808.Source: Mifflin et al. 1990; 3,500 kcal per lb (Wishnofsky 1958); closed-form solution in content.mdx
  2. Sex Male, Age 40, Height 5 ft 10.9 in, Weight 220.5 lb, Activity Moderate: exercise 3 to 5 days, BMR formula Mifflin-St Jeor, Goal weight 198.4 lb, Calories you eat a day 2,000, Start date 2027-01-01 gives Calories you burn now (TDEE) 2,991.5, Daily deficit now 991.5, Weeks to your goal 12.089327, You reach your goal on 2027-03-27, Weeks by the 3,500-calorie rule 11.117613.Source: Mifflin et al. 1990; 3,500 kcal per lb; hand calculation in content.mdx
  3. Sex Female, Age 50, Height 5 ft 5 in, Weight 176.4 lb, Activity Sedentary: little or no exercise, BMR formula Harris-Benedict, Goal weight 165.3 lb, Calories you eat a day 1,300, Start date 2026-09-27 gives Calories you burn now (TDEE) 1,778.4276, Weeks to your goal 12.244724, Days to your goal 86, You reach your goal on 2026-12-22.Source: Roza and Shizgal 1984 (revised Harris-Benedict); 3,500 kcal per lb; hand calculation in content.mdx

How it works

Daily needs. Your total daily energy expenditure (TDEE) at weight w (kg) is TDEE(w) = f × BMR(w), where f is the activity factor (1.2 sedentary, 1.375 light, 1.55 moderate, 1.725 very active, 1.9 extra active). BMR uses height in centimetres and age in years:

  • Mifflin-St Jeor (default): men 10 × w + 6.25 × height − 5 × age + 5; women 10 × w + 6.25 × height − 5 × age − 161.
  • Revised Harris-Benedict (under "More options"): men 88.362 + 13.397 × w + 4.799 × height − 5.677 × age; women 447.593 + 9.247 × w + 3.098 × height − 4.330 × age.

Call a the weight coefficient of the chosen BMR formula: 10 for Mifflin-St Jeor, 13.397 (men) or 9.247 (women) for Harris-Benedict. Each kilogram you lose lowers your TDEE by s = f × a calories a day.

Energy balance. A kilogram of body weight is taken as K = 3,500 ÷ 0.45359237 = 7,716.18 calories (3,500 per pound; Wishnofsky, 1958). You eat I calories a day. The daily deficit is D = TDEE(w) − I, and weight falls at D ÷ K kilograms a day. Because D shrinks by s for each kilogram lost, the deficit falls smoothly:

D(t) = D₀ × e^(−t ÷ τ), with τ = K ÷ s days

where D₀ = TDEE(current weight) − I is the deficit on day 0 and t is in days.

Time to the goal. At the goal weight g the deficit is D_g = TDEE(g) − I = D₀ − s × (current weight − g). Then:

days to goal = τ × ln(D₀ ÷ D_g)

  • Weeks to goal = days ÷ 7.
  • The goal date is the start date plus the days, rounded up to a whole day.
  • Loss in the first week = (D₀ ÷ s) × (1 − e^(−7 ÷ τ)).
  • For comparison, weeks by the 3,500-calorie rule = (current weight − g) × K ÷ D₀ ÷ 7, as if the deficit stayed at D₀.

No answer when the goal is not below your current weight; when D₀ is 0 or less (you would not lose weight at this intake); when D_g is 0 or less (your weight levels off at current weight − D₀ ÷ s, above the goal); or when it would take more than 3,652 days (10 years).

A note warns you when the daily intake is under 1,200 calories (women) or 1,500 (men), the low end of the weight-loss diets in the 2013 AHA/ACC/TOS guideline. It reads exactly: "1,100 calories a day is under 1,200, below the lowest diet the weight-loss guideline suggests. Ask a doctor first.", with your intake and limit as whole numbers with thousands separators.

The chart shows the weeks to your goal for daily intakes from 800 to 3,000 calories, with everything else as you entered it.

Assumptions

  • The model is a simple energy balance. Real bodies adapt further during a diet (Hall and others, 2011), so real loss is often slower.
  • Age, height and activity stay as entered for the whole time.
  • The formulas are for adults. They do not apply to children, or during pregnancy or breastfeeding.
  • Nothing is rounded until the result is shown, except the goal date, which rounds the days up.
  • This calculator gives an estimate for planning. It is not medical advice. Talk to a doctor or a registered dietitian before you start a diet.

Worked examples by hand

A 30-year-old woman, 5 ft 5 in (165.1 cm), lightly active, from 150 lb (68.039 kg) to 140 lb (63.503 kg) on 1,500 calories a day, starting October 1, 2026. BMR = 680.39 + 1,031.88 − 150 − 161 = 1,401.26. TDEE = 1,401.26 × 1.375 = 1,926.74. D₀ = 1,926.74 − 1,500 = 426.74. s = 1.375 × 10 = 13.75, so τ = 7,716.18 ÷ 13.75 = 561.18 days. She loses 10 lb = 4.536 kg, so D_g = 426.74 − 13.75 × 4.536 = 364.37 (her TDEE at 140 lb is 1,864.37). Days = 561.18 × ln(426.74 ÷ 364.37) = 561.18 × 0.15800 = 88.67, which is 12.67 weeks. Rounded up to 89 days, she reaches 140 lb on December 29, 2026. First week: (426.74 ÷ 13.75) × (1 − e^(−7 ÷ 561.18)) = 31.04 × 0.012396 = 0.385 kg (0.85 lb). By the 3,500-calorie rule it would be 10 × 3,500 ÷ 426.74 ÷ 7 = 11.72 weeks.

A 40-year-old man, 180 cm, moderately active, from 100 kg to 90 kg on 2,000 calories a day, starting January 1, 2027. BMR = 1,000 + 1,125 − 200 + 5 = 1,930. TDEE = 1,930 × 1.55 = 2,991.5. D₀ = 991.5. s = 1.55 × 10 = 15.5, τ = 497.82 days. D_g = 991.5 − 15.5 × 10 = 836.5. Days = 497.82 × ln(991.5 ÷ 836.5) = 84.63, 12.09 weeks; 85 days after January 1, 2027 is March 27, 2027. The 3,500-calorie rule gives 11.12 weeks.

Harris-Benedict: a 50-year-old woman, 165 cm, sedentary, from 80 kg to 75 kg on 1,300 calories a day, starting September 27, 2026. BMR = 447.593 + 9.247 × 80 + 3.098 × 165 − 4.330 × 50 = 1,482.02. TDEE = 1,482.02 × 1.2 = 1,778.43. D₀ = 478.43. s = 1.2 × 9.247 = 11.096, τ = 695.38 days. D_g = 478.43 − 11.096 × 5 = 422.95. Days = 695.38 × ln(478.43 ÷ 422.95) = 85.71, 12.24 weeks, rounded up to 86 days: December 22, 2026.

Other questions people ask

How long will it take to reach my goal weight?

It depends on the gap between the calories you burn and the calories you eat. For example, a 30-year-old woman who is 5 ft 5 in, 150 lb and lightly active burns about 1,927 calories a day. Eating 1,500 a day, she reaches 140 lb in about 12.7 weeks.

Why is this slower than the 3,500-calorie rule?

The 3,500-calorie rule assumes your deficit stays the same. But a lighter body burns fewer calories, so the same intake gives a smaller deficit each week. This calculator lets your needs fall as your weight falls, so the time to your goal is longer. Researchers at the NIH and elsewhere found that the fixed rule overestimates weight loss over months.

Why does it say my weight levels off before my goal?

At a fixed intake, your weight moves toward the weight at which you burn exactly what you eat. If that weight is above your goal, you would never reach the goal at that intake. Eat fewer calories, or choose a higher activity level if you really are more active.

How fast is it safe to lose weight?

The CDC notes that people who lose about 1 to 2 pounds a week are more likely to keep the weight off. The 2013 AHA/ACC/TOS guideline suggests diets of 1,200 to 1,500 calories a day for women and 1,500 to 1,800 for men. The calculator warns you when your intake is under 1,200 (women) or 1,500 (men).

What does the chart show?

It shows the weeks to your goal for daily intakes from 800 to 3,000 calories, with everything else as you entered it. Eating a little less shortens the time a lot when you are close to your needs. Where the line stops, that intake never reaches the goal.

Is this calculator accurate for me?

It is an estimate from average equations. Your real needs can differ by 10% or more, and bodies also adapt to dieting in ways this model leaves out, so real loss is often slower still. Weigh yourself weekly and adjust.