# What is my weight loss timeline?

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.

- Page: https://www.acalculator.org/health/weight-loss-calculator
- JSON spec: https://www.acalculator.org/health/weight-loss-calculator.json
- Version: 0fee177a8750

## Default answer

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.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| sex | Sex | Sex at birth, which the body formulas use. |
| age | Age | Your age in whole years. |
| height | Height | Your height without shoes. |
| weight | Weight | Your body weight. |
| activity | Activity | How active you are in a usual week, which sets the multiplier on your BMR. |
| goal | Goal weight | The weight you want to reach. |
| intake | Calories you eat a day | The calories you plan to eat each day until you reach your goal. |
| start | Start date | The day you start. Today, unless you change it. |
| formula | BMR formula | The equation for basal metabolic rate: Mifflin-St Jeor (1990) or the revised Harris-Benedict (1984). |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| date | You reach your goal on | The date you reach the goal weight: the start date plus the days to the goal, rounded up. |
| weeks | Weeks to your goal | Time to the goal weight in weeks, with daily needs falling as weight falls. |
| days | Days to your goal | Time to the goal weight in whole days, rounded up. |
| tdee | Calories you burn now (TDEE) | Total daily energy expenditure at your current weight: BMR × activity factor. |
| deficit | Daily deficit now | TDEE at your current weight minus the calories you eat. |
| tdeeGoal | Calories you burn at your goal weight | TDEE at the goal weight, which is lower, so the deficit shrinks as you lose. |
| firstWeek | Loss in the first week | Weight lost in the first 7 days. |
| simpleWeeks | Weeks by the 3,500-calorie rule | Weeks to the goal if the deficit stayed at its starting size: the simple 3,500-calories-per-pound rule. |
| limit | Note | A warning when the daily intake is below the lowest intake the weight-loss guideline suggests. |

## 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).

## Assumptions

- 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.

## Worked examples

1. sex = female, age = 30, height = 1.651, weight = 68.038856, activity = light, formula = mifflin, goal = 63.502932, intake = 1,500, start = 2026-10-01 gives tdee = 1,926.737388, deficit = 426.737388, tdeeGoal = 1,864.368437, weeks = 12.666821, days = 89, date = 2026-12-29, firstWeek = 0.384725, simpleWeeks = 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 = 1.8, weight = 100, activity = moderate, formula = mifflin, goal = 90, intake = 2,000, start = 2027-01-01 gives tdee = 2,991.5, deficit = 991.5, weeks = 12.089327, date = 2027-03-27, simpleWeeks = 11.117613. Source: Mifflin et al. 1990; 3,500 kcal per lb; hand calculation in content.mdx.
3. sex = female, age = 50, height = 1.65, weight = 80, activity = sedentary, formula = harris, goal = 75, intake = 1,300, start = 2026-09-27 gives tdee = 1,778.4276, weeks = 12.244724, days = 86, date = 2026-12-22. Source: Roza and Shizgal 1984 (revised Harris-Benedict); 3,500 kcal per lb; hand calculation in content.mdx.

## FAQ

### 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.

## Sources

- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247. https://doi.org/10.1093/ajcn/51.2.241
- Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. Am J Clin Nutr. 1984;40(1):168-182. https://doi.org/10.1093/ajcn/40.1.168
- FAO/WHO/UNU. Human energy requirements (2004), section 5.3.1, Classification of physical activity levels (PAL = TEE ÷ BMR). https://www.fao.org/4/y5686e/y5686e07.htm
- Wishnofsky M. Caloric equivalents of gained or lost weight. Am J Clin Nutr. 1958;6(5):542-546. https://doi.org/10.1093/ajcn/6.5.542
- Hall KD, Sacks G, Chandramohan D, et al. Quantification of the effect of energy imbalance on bodyweight. Lancet. 2011;378(9793):826-837. https://doi.org/10.1016/S0140-6736(11)60812-X
- Thomas DM, et al. Can a weight loss of one pound a week be achieved with a 3500-kcal deficit? Commentary on a commonly accepted rule. Int J Obes. 2013;37(12):1611-1613. https://doi.org/10.1038/ijo.2013.51
- Jensen MD, Ryan DH, Apovian CM, et al. 2013 AHA/ACC/TOS Guideline for the Management of Overweight and Obesity in Adults. Circulation. 2014;129(25 Suppl 2):S102-S138. https://pmc.ncbi.nlm.nih.gov/articles/PMC5819889/
- Centers for Disease Control and Prevention. Steps for Losing Weight. https://www.cdc.gov/healthy-weight-growth/losing-weight/index.html