Answer first
What this calculator tells you
Estimate the weeks needed to reach a goal weight at a steady daily calorie deficit. Treat the date as a rough plan, since the 3,500 calorie rule overstates loss as your body adapts. Formula: Weeks = (current weight − goal weight) × 3,500 kcal ÷ (daily deficit × 7). At the worked-example inputs, the weeks to goal is 20. Holding every other input steady, moving current weight (lb) from 144 to 216 moves the result from 0 to 56.
Transparent method
The formula
Treat the date as a rough plan, since the 3,500 calorie rule overstates loss as your body adapts.
Worked example
Example inputs
How to interpret the result
The 3,500-calorie-per-pound rule turns a daily deficit into a date. Cutting 500 calories a day for 20 pounds lands at 20 weeks on paper. Real loss starts faster and then slows, because a lighter body burns less and the body adapts. So the paper date is the earliest reasonable finish, and the true one usually runs later.
At the worked-example inputs the weeks to goal is 20. It rises with current weight (lb) and falls as goal weight (lb) and daily calorie deficit increase.
Calorie and macronutrient needs vary with metabolism, health conditions, medication and real-world activity that a formula cannot measure. Treat the result as a starting estimate, adjust based on actual results, and consult a registered dietitian or physician before a major dietary change.
Before you rely on it
What to check
Recheck the deficit against your own maintenance calories every few weeks. A shrinking body needs a smaller deficit target to keep the same pace.
The common error
Where people go wrong with weight loss time calculator
Doubling the deficit to hit the date sooner. Very large deficits cost muscle and are hard to hold, and the extra loss rarely arrives in proportion.
Sensitivity evidence
How current weight (lb) changes the weeks to goal
Holding every other input at the worked-example value, moving current weight (lb) from 144 to 216 moves the weeks to goal from 0 to 56: a spread of 56, or 280% of the worked-example result.
| Current weight (lb) | Weeks to goal | Total calorie deficit needed |
|---|---|---|
| 144 | 0 | 0 |
| 162 | 2 | 7,000 |
| 180worked example | 20 | 70,000 |
| 198 | 38 | 133,000 |
| 216 | 56 | 196,000 |
Every input, tested
Which input moves the weeks to goal most
Of the 3 inputs, current weight (lb) moves the weeks to goal most (36 across the range tested) and daily calorie deficit moves it least (4).
| Input | Tested from | To | Weeks to goal at each end | Swing |
|---|---|---|---|---|
| Current weight (lb) | 162 | 198 | 2 to 38 | 36 (180%) |
| Goal weight (lb) | 144 | 176 | 36 to 4 | 32 (160%) |
| Daily calorie deficit | 450 | 550 | 22.2 to 18.2 | 4 (20%) |
Two variables at once
Weeks to goal by current weight (lb) and goal weight (lb)
Across the grid the weeks to goal runs from 0 to 88. Moving current weight (lb) from 144 to 216 shifts it by 56 at the middle column, and moving goal weight (lb) from 128 to 192 shifts it by 52 at the middle row, so current weight (lb) is the bigger lever here.
| Current weight (lb) \ Goal weight (lb) | 128 | 160 | 192 |
|---|---|---|---|
| 144 | 16 | 0 | 0 |
| 162 | 34 | 2 | 0 |
| 180 | 52 | 20 | 0 |
| 198 | 70 | 38 | 6 |
| 216 | 88 | 56 | 24 |
The highlighted cell is the worked example: 20.
Step by step
The worked example, input by input
| Input | Value used | What it means |
|---|---|---|
| Current weight (lb) | 180 | Your weight today, in pounds. |
| Goal weight (lb) | 160 | The weight you want to reach, in pounds. |
| Daily calorie deficit | 500 | How many calories below maintenance you eat or burn off each day. |
| Weeks to goal | 20 | |
| Total calorie deficit needed | 70,000 | |
Inputs, definitions and assumptions
Current weight (lb)
Your weight today, in pounds. The prefilled worked-example value is 180.
Goal weight (lb)
The weight you want to reach, in pounds. The prefilled worked-example value is 160.
Daily calorie deficit
How many calories below maintenance you eat or burn off each day. The prefilled worked-example value is 500.
How to use this calculator
- 1Verify the inputs. Gather current weight (lb), goal weight (lb) and daily calorie deficit from your own documents; the prefilled values are examples.
- 2Save a baseline. The worked example puts the weeks to goal at 20. Store your own version of it as Scenario A.
- 3Test one change. Start with current weight (lb), the input with the biggest effect here: moving current weight (lb) from 162 to 198 takes the weeks to goal from 2 to 38, a swing of 180% of the worked-example figure.
- 4Check the extremes. At half the example current weight (lb) (90) the weeks to goal is 0; at double (360) it is 200.
People also ask
Frequently asked questions
How do you calculate weight loss time?
Weeks = (current weight − goal weight) × 3,500 kcal ÷ (daily deficit × 7). At the worked-example inputs the weeks to goal is 20.
What does the weight loss time result mean?
Treat the date as a rough plan, since the 3,500 calorie rule overstates loss as your body adapts. At the worked-example inputs the weeks to goal is 20. It rises with current weight (lb) and falls as goal weight (lb) and daily calorie deficit increase.
How much does current weight (lb) change the weeks to goal?
Holding every other input at the worked-example value, moving current weight (lb) from 144 to 216 moves the weeks to goal from 0 to 56, a spread of 56.
What are the limits of this weight loss time calculator?
Calorie and macronutrient needs vary with metabolism, health conditions, medication and real-world activity that a formula cannot measure. Treat the result as a starting estimate, adjust based on actual results, and consult a registered dietitian or physician before a major dietary change. The tables on this page test current weight (lb) only from 144 to 216; a value outside that range is not tabulated here.
Which input moves the weeks to goal most in the weight loss time calculator?
Ranked by how far each moves the weeks to goal across the range tested: current weight (lb) (36, 180%), goal weight (lb) (32, 160%) and daily calorie deficit (4, 20%).
If I double current weight (lb) in the weight loss time calculator, does the weeks to goal double?
Doubling it from 180 to 360 takes the weeks to goal from 20 to 200, which is 10.00 times the worked-example figure. So the result grows faster than the input does. Halving it to 90 gives 0.
How much does goal weight (lb) matter in the weight loss time calculator?
The worked example uses 160. Holding every other input at its worked-example value, moving goal weight (lb) from 144 to 176 takes the weeks to goal from 36 to 4, a swing of 160% of the worked-example figure.
How much does daily calorie deficit matter in the weight loss time calculator?
The worked example uses 500. With the other inputs left at the worked example, moving daily calorie deficit from 450 to 550 takes the weeks to goal from 22.2 to 18.2, a swing of 20% of the worked-example figure.
Which inputs change the total calorie deficit needed in the weight loss time calculator?
At the worked-example inputs it is 70,000. Current weight (lb) takes it from 7,000 to 133,000 and goal weight (lb) takes it from 126,000 to 14,000.
Is the 3,500-calorie-per-pound rule accurate?
It is a long-standing approximation, not an exact physiological constant. It is less accurate at larger deficits and over longer periods as metabolism adapts. It is useful for a rough estimate, not a precise prediction.
Sources and evidence
Free Calculators Online is independent and is not affiliated with or endorsed by the source organizations. Educational estimates only.