UK · stone, pounds and kilograms
Weight loss calculator. How long will it take?
Enter your current and target weight, and see how long it could take, in stone, pounds or kilograms.
- NHS-sourced thresholds
- Method published in full
- Nothing leaves your device
Right now I weigh st lb, and I want to be st lb. I’m , , and cm tall. Most weeks I’m , and I’d like to go at a pace.
4blanks still to fill
Examplesomeone at 16 st 4 lb aiming for 13 st 7 lb
Estimated timeframe
7-14months
Fill in the sentence above and this becomes yours, with the projected path, the milestones on the way, and what a different pace would cost.
- To lose
- 2 st 11 lb
- 17.1% of body weight
- Daily target
- 1,850
- kcal · 550 deficit
- Maintenance
- 2,400
- kcal a day
- Current BMI
- 35.8
- Obese (class 2)
What do my results mean?
- Estimated timeframe
- A range, not a date. It is how long the calculation suggests your goal could take if you stay close to your calorie target. Real progress varies, so we show a span rather than a single day.
- Maintenance calories
- Roughly what you would eat to stay at your current weight, given your estimated activity level.
- Daily calorie target
- Your maintenance figure minus the daily deficit implied by the pace you chose. It is the amount to eat each day, not your target weight.
- Milestones
- Points along the way that are worth noticing. A 5% reduction in body weight is associated with meaningful health benefits, and it arrives far sooner than a final goal.
Why the estimate is a range
Two people with identical measurements can lose weight at noticeably different rates. Rather than pick one number and present it as fact, this calculator runs the projection under a more and a less favourable set of assumptions and shows you the span between them.
How is this calculated?
First we estimate your basal metabolic rate, the energy your body uses at rest, using the Mifflin-St Jeor equation[American Journal of Clinical Nutrition]. That is multiplied by an activity factor to estimate your total daily energy expenditure, and your calorie target is that figure minus a daily deficit.
Men: (10 × kg) + (6.25 × cm) − (5 × age) + 5 Women: (10 × kg) + (6.25 × cm) − (5 × age) − 161Why we do not simply divide by 7,700
Most weight loss calculators take the gap between your current and target weight, multiply it by about 7,700 kcal per kilogram, divide by your daily deficit and print the answer. That assumes your energy needs never change. They do: as you get lighter, your body needs less energy, so the same calorie target produces a smaller and smaller deficit.
Instead, this calculator simulates your progress week by week, recalculating your energy needs at your new weight each time, and assumes you revisit your target every few weeks as the simulation does. It runs that simulation three times under different assumptions about how closely a plan is followed and how much metabolism adapts, and reports the span between the quickest and slowest results.
Every formula, multiplier and assumption is written out in full on our methodology page, including the ones we think are uncertain.
What this calculator cannot tell you
Like every weight loss calculator, this one produces estimates built on population averages. It cannot account for:
- How your individual metabolism differs from the equation average: the spread between people is substantial.
- Body composition. Two people at the same weight and height can have very different amounts of muscle.
- Water weight, which usually makes the first week or two look faster than any steady model predicts, and which fluctuates by a kilogram or more day to day.
- Medication, including weight-management medicines, and health conditions such as thyroid disorders or PCOS.
- Hormonal changes, including the menstrual cycle, pregnancy and the menopause.
- How closely anyone actually sticks to a calorie target over months.
A projection is not a promise
The line on the chart is what the arithmetic produces if everything holds steady. Nobody loses weight in a smooth curve. Use it to get a sense of scale, not to hold yourself to a schedule.
Understand your numbers
Four figures do most of the work in any weight-loss estimate. Each has its own calculator if you want to look at it on its own.
- BMIBody mass indexYour weight relative to your height, and the category it falls in.
- BMRBasal metabolic rateThe energy your body uses at rest, before you move at all.
- TDEETotal daily energyYour BMR plus everything else you do in a day.
- DeficitCalorie deficitThe gap between what you burn and what you eat.
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Frequently asked questions
How long does it take to lose a stone?
At the pace the NHS describes as safe (0.5 to 1 kg, or 1 to 2 lb, a week) a stone takes somewhere between about seven and fourteen weeks. Where you fall in that span depends on your starting weight, your activity level and how consistently the deficit is maintained.
Heavier people tend to lose faster at the start, because a larger body burns more energy, and the rate naturally eases as weight comes down. Enter your current and target weight above for an estimate based on your own measurements rather than an average.
How many calories should I eat to lose weight?
The NHS suggests reducing intake by around 600 kcal a day from what you need to maintain your weight[NHS Better Health]. As a general reference it puts average daily needs at roughly 2,000 kcal for women and 2,500 kcal for men, but your own maintenance figure depends on your size, age and activity.
The calculator works out your estimated maintenance figure and subtracts the deficit implied by the pace you choose, rather than applying a one-size-fits-all number.
Should I choose the fastest option?
Not necessarily. None of these paces is faster than the range the NHS describes as safe, and the gentle option is deliberately slower than it: at 0.25 kg a week it sits below the bottom of the NHS band, because a pace you can keep beats one you abandon. A faster pace means a larger daily deficit, which is harder to sustain. The pace that works is the one you can still be following in six months.
Why do you show a range instead of a date?
Because the underlying estimate does not support more precision than that. The inputs are population equations with real error margins, and nobody follows a calorie target perfectly. A specific date would look more authoritative and be less honest.
Do you store my weight?
No. Every calculation runs in your browser. Your measurements are never sent to us, and they are never included in our analytics. If you come back, your entries are restored from your own device, and the "Start again" button clears them.
Sources
- Overweight and obesity in adults, NHS
- Calories and weight loss, NHS Better Health
- A new predictive equation for resting energy expenditure in healthy individuals, American Journal of Clinical Nutrition
- Overweight and obesity management (NG246), NICE
Important information
The calculators on this site provide general information and estimates. They are not medical advice and they do not diagnose any condition.
Everyone is different, and individual energy needs vary for reasons these equations cannot capture. If you have a health condition, take medication, are pregnant or breastfeeding, or have any concerns about your weight, speak to your GP, pharmacist or a registered dietitian.