Weight Loss Timeline Calculator
When you'll actually hit your goal weight at a given calorie deficit — the naive 3,500 kcal date plus a slower, realistic one that accounts for the plateau.
Weight Loss Timeline Calculator: with the default inputs, realistic goal date is May 21, 2027.
How far below maintenance you eat, on average. 500 kcal/day is the classic 1 lb-a-week target.
Adaptive model — accounts for maintenance falling as you get lighter.
- Weeks to goal (realistic)
- 36
- Date the 3,500 kcal rule predicts
- March 4, 2027The optimistic linear estimate almost every calculator gives.
- Weeks to goal (linear rule)
- 25
- Extra weeks the slowdown costs
- 11
- Total to lose
- 25 lb
- Weight this deficit eventually settles at
- 153.9 lbWhere loss stops if you hold this deficit forever and change nothing else.
- Expected loss in the first month
- 4.1 lb
- BMI at your goal weight
- 25.1
Assumptions
- The linear estimate uses Wishnofsky's 3,500 kcal per pound (7,716 kcal per kg) of body weight.
- The realistic estimate approaches the plateau from Hall et al. (2011) — about 1 kg of eventual change per 100 kJ/day of intake change — with a 322.8-day time constant chosen so the initial rate matches the linear rule.
- A single exponential is a simplification of a two-timescale physiological model; Hall's full model puts roughly half the eventual change at one year, where this fit puts it nearer seven months.
- It assumes the deficit is held constant and nothing else changes — no training block, medication, illness, or unconscious drift in intake.
- This is an estimate for healthy adults, not medical advice, and it is not appropriate for pregnancy, childhood, or anyone in treatment for an eating disorder.
| Month | Date | Realistic weight(lb) | 3,500 kcal rule(lb) |
|---|---|---|---|
| 0 | September 10, 2026 | 200 lb | 200 lb |
| 1 | October 10, 2026 | 195.9 lb | 195.7 lb |
| 2 | November 9, 2026 | 192.2 lb | 191.4 lb |
| 3 | December 9, 2026 | 188.8 lb | 187.1 lb |
| 4 | January 8, 2027 | 185.7 lb | 182.9 lb |
| 5 | February 7, 2027 | 182.9 lb | 178.6 lb |
| 6 | March 9, 2027 | 180.3 lb | 174.3 lb |
| 7 | April 8, 2027 | 177.9 lb | 170 lb |
| 8 | May 8, 2027 | 175.8 lb | 165.7 lb |
| 9 | June 7, 2027 | 173.9 lb | 161.4 lb |
| 10 | July 7, 2027 | 172.1 lb | 157.1 lb |
| 11 | August 6, 2027 | 170.5 lb | 152.9 lb |
| 12 | September 5, 2027 | 169 lb | 148.6 lb |
The two columns separate over time. That gap is the whole point: the linear rule keeps subtracting the same amount forever, while your maintenance calories fall as you get lighter.
How this is worked out
The formula
Linear (Wishnofsky, 1958): days = weight to lose (kg) × 7,716 kcal/kg ÷ daily deficit Adaptive (fitted to Hall et al., 2011): plateau loss = 0.04184 kg × daily deficit (100 kJ/day ≈ 1 kg eventual change) loss(t) = plateau loss × (1 − e^(−t / 322.8 days)) days to goal = −322.8 × ln(1 − weight to lose ÷ plateau loss) The 322.8-day time constant is set so the initial rate of loss matches the 3,500 kcal/lb rule.
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- Current weight
- A number.in lb, kg, st · from 50 to 1000 · defaults to 200
- Goal weight
- A number.in lb, kg, st · from 50 to 1000 · defaults to 175
- Daily calorie deficit
- How far below maintenance you eat, on average. 500 kcal/day is the classic 1 lb-a-week target.from 50 to 1500 · defaults to 500
- Start date
- A calendar date.defaults to today
- Height(under More options)
- Optional. Used only to check that the goal weight sits in a healthy BMI range.in ft, in, cm, m · from 3 to 8.5 · defaults to 5.8333
What you get back
- Realistic goal datemain answer
- Adaptive model — accounts for maintenance falling as you get lighter.
- Weeks to goal (realistic)
- Date the 3,500 kcal rule predicts
- The optimistic linear estimate almost every calculator gives.
- Weeks to goal (linear rule)
- Extra weeks the slowdown costs
- Total to lose
- Weight this deficit eventually settles at
- Where loss stops if you hold this deficit forever and change nothing else.
- Expected loss in the first month
- BMI at your goal weight
What this assumes
- The linear estimate uses Wishnofsky's 3,500 kcal per pound (7,716 kcal per kg) of body weight.
- The realistic estimate approaches the plateau from Hall et al. (2011) — about 1 kg of eventual change per 100 kJ/day of intake change — with a 322.8-day time constant chosen so the initial rate matches the linear rule.
- A single exponential is a simplification of a two-timescale physiological model; Hall's full model puts roughly half the eventual change at one year, where this fit puts it nearer seven months.
- It assumes the deficit is held constant and nothing else changes — no training block, medication, illness, or unconscious drift in intake.
- This is an estimate for healthy adults, not medical advice, and it is not appropriate for pregnancy, childhood, or anyone in treatment for an eating disorder.
About this calculator
Almost every weight-loss calculator does the same sum: pounds to lose, times 3,500 calories, divided by your daily deficit. It gives a date, and the date is wrong — reliably, predictably, in the same direction. This one shows you both: the number that rule produces, and a second date that accounts for the fact that a lighter body burns fewer calories.
Why the 3,500-calorie rule overshoots
Max Wishnofsky worked out in 1958 that a pound of body fat stores about 3,500 kcal. That part is fine. The mistake is treating your deficit as fixed. As you lose weight you carry less tissue around, your resting metabolism drops, and moving costs less — so a diet that started 500 kcal below maintenance is only 400 below it twenty pounds later, then 300, and eventually zero. That last point is the plateau, and it is not a failure of willpower. It is arithmetic.
Kevin Hall's group quantified it: a permanent change of about 100 kJ a day in intake produces roughly 1 kg of eventual weight change, and the change arrives slowly, over years rather than months. This calculator uses that as the destination and the classic 3,500 kcal figure as the starting speed, joining them with a single exponential.
How to use it
Enter your current weight, your goal, and the daily deficit you can actually hold — not the one you can hold for a fortnight. Under More options, adding your height lets the calculator check that the goal weight lands in a healthy BMI range. The start date defaults to today.
Reading the results
- The realistic goal date is the headline. For a 25 lb loss at 500 kcal a day it lands around eleven weeks later than the linear rule predicts.
- The plateau is where this deficit stops working. A 500 kcal deficit eventually settles about 46 lb below your starting weight; if your goal is further than that, the calculator says so rather than inventing a date, and tells you the deficit that would get there.
- First-month loss is deliberately shown separately, because the first few weeks include glycogen and the water bound to it — often 2–4 lb that is not fat and will not repeat.
- The month-by-month table shows the two models diverging. Print it, ignore the daily scale, and check yourself against the monthly line.
What this cannot see
It assumes you hold the deficit, that nothing else changes, and that your maintenance follows the population average. It cannot see sleep, medication, thyroid function, menstrual water shifts, a new training block, or the ordinary fact that appetite fights back — the Hall model's slow arrival is partly a description of people unconsciously eating a little more as they get lighter. A date from a formula is a planning tool. Weight loss that sticks is measured in years and habits, not in the accuracy of a projection.
If you find yourself setting a goal below a BMI of 18.5, or chasing a date hard enough that meals get skipped, that is worth a conversation with a doctor or a dietitian rather than a faster calculator.
Frequently asked questions
▸How long will it take to lose 20 pounds?
At a 500 kcal daily deficit the 3,500-calorie rule says 20 weeks. Accounting for the slowdown as you get lighter, expect closer to 26 weeks — about six months. The larger the loss, the wider that gap.
▸Why does weight loss stall?
Because your maintenance calories fall with your weight. A deficit of 500 kcal a day shrinks to nothing once you are roughly 46 lb lighter, which is exactly where this model says loss stops. Getting past it needs a bigger deficit or more activity, not more discipline.
▸Is 2 pounds a week realistic?
It needs a 1,000 kcal daily deficit, which for most people means eating near or below their resting metabolic rate. It works briefly for people with a lot to lose and rarely for anyone else. Around 0.5–1% of body weight a week is the range that keeps muscle.
▸Why is my first month faster than the calculator says?
Early loss includes glycogen and the water stored with it — typically 2–4 lb in the first week or two that never repeats. The projection deliberately does not credit that as fat, so real scales usually run ahead of it at first and catch up by month two.
▸Should I recalculate as I lose weight?
You do not need to for this tool — the adaptive model already builds the slowdown in. Do re-check your maintenance calories every 10–15 lb, because the deficit you are actually running depends on it.
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