A weight loss calculator by date that slows down like real life
This weight loss calculator answers the two questions people ask most: “If I eat this many calories a day, when will I reach my goal weight?” and “How many calories a day do I need to reach my goal by a date — a wedding, a holiday, a new year?” Enter your age, sex, height, weight, goal and activity level and you get a date, a week-by-week projection and a chart.
Most calculators divide the weight you want to lose by a fixed 7,700 kcal per kilogram (3,500 kcal per pound) and draw a straight line. That overstates progress: as you get lighter you burn fewer calories, so the same intake gives a smaller deficit. This tool recalculates your maintenance calories every day from your new weight, so the curve flattens, and shows the simple straight line beside it for comparison. It works the same for women and men, in metric or imperial units.
How to use the Weight Loss Calculator
- Choose When will I reach my goal? or Calories to reach it by a date.
- Select units and sex, then enter age, height, current weight, goal weight and activity level.
- Set the start date, then either the calories you plan to eat or your goal date.
- Read the result, the warnings (if any), the chart and the week-by-week table.
- Re-run it every few weeks with your real weight — the projection is only as good as the inputs.
Weight Loss Calculator features
Two directions
Goal date from daily calories, or daily calories from a goal date.
Adaptive projection
Maintenance calories (Mifflin-St Jeor × activity) are recalculated each day as weight falls.
Safety checks
Flags intakes under 1,200/1,500 kcal, very-low-calorie diets under 800 kcal, losses above 1 kg (2 lb) a week, and goals below a healthy BMI.
Chart and table
A projected weight curve with your goal line, and maintenance and deficit every four weeks.
Metric or imperial
Centimetres and kilograms or feet, inches and pounds.
How the projection is calculated
Maintenance. Resting energy uses the Mifflin-St Jeor equation — 10 × weight (kg) + 6.25 × height (cm) − 5 × age, + 5 for men or − 161 for women — multiplied by an activity factor from 1.2 (sedentary) to 1.9 (extra active), as in the calorie calculator.
Each day the gap between maintenance and what you eat is converted to weight at 7,700 kcal per kg, and maintenance is recalculated from the new weight. In “by date” mode the tool searches for the steady daily intake that lands exactly on your goal on that date.
Example: a 35-year-old woman, 165 cm and 80 kg, lightly active, has a maintenance of about 2,056 kcal. Eating 1,600 kcal a day she loses about 0.4 kg a week at first; the simple rule says 10 kg takes about 24 weeks, while the adaptive projection takes roughly 29 weeks because the deficit shrinks.
Safe rate of weight loss
NHS guidance is to aim for 0.5–1 kg (1–2 lb) a week, usually by eating about 600 kcal a day less than you need. Faster loss means more muscle loss, gallstones and fatigue, and is harder to keep off. Very-low-calorie diets of under 800 kcal a day are not suitable for everyone and should only be followed with medical supervision. If the date you want needs more than that, choose a later date and add activity — the calories burned calculator shows what exercise adds.
Why real results differ
- The first week often shows a bigger drop from water and stored carbohydrate, not fat.
- Metabolism slows a little more than weight alone predicts (adaptive thermogenesis); research models such as the NIH Body Weight Planner include this and body-composition changes, which this simplified model does not.
- Tracking errors are common — oils, drinks and snacks are easy to miss. Weigh weekly and compare the trend with the table.
- A goal that is a healthy weight for your height matters more than the date; check it with the BMI calculator.
Weight Loss Calculator FAQ
How do I calculate when I will reach my goal weight?
Enter your details, goal weight and planned daily calories with “When will I reach my goal?”. The calculator simulates each day, recalculating your maintenance calories as you lose, and gives the date you reach the goal.
How many calories should I eat to lose weight by a certain date?
Switch to “Calories to reach it by a date” and pick the date. It solves for the steady daily intake that reaches your goal on that day and warns you if that is below a safe level.
Is this weight loss calculator suitable for women?
Yes. It uses the female version of the Mifflin-St Jeor equation and the usual 1,200 kcal minimum for women. It is not for pregnancy or breastfeeding — ask your midwife or doctor then.
Why is the date later than other calculators?
Many use a straight 7,700 kcal-per-kg rule with today’s calorie needs. Your needs fall as you lose weight, so loss slows; this calculator includes that, and shows the straight-line estimate for comparison.
Is it free and private?
Yes. It runs in your browser, needs no sign-up, and your entries are stored only on this device.
Is this medical advice?
No. It is an estimate for healthy adults. Talk to a doctor or registered dietitian if you have a health condition, take medicines that affect weight, or plan a very-low-calorie diet.