Weight Loss Calculator

What a goal weight needs to become a plan

A number on the scale is not a plan until three more numbers exist: how many pounds separate you from the goal, how fast you intend to close the gap, and what you eat each day while doing it. This calculator runs that chain in order. Give it the current weight, the goal weight, the basics the burn formula needs, and a pace, and it returns the deficit in calories, the daily intake that produces the deficit, the number of weeks the pace implies, and the date the goal lands on the calendar. Change the pace and every downstream number moves with it.

The order matters because the common failure runs backward. People pick a date, divide the pounds by the days, and end up with a pace nobody can hold. Picking the pace first, checking it against the public health guidance, and letting the date fall where it may is the sequence that survives contact with a real kitchen. The calculator shows the check explicitly: if your pace would push intake below the published floors, the results panel says so and shows the intake at the floor instead, with the slower pace that goes with it.

From goal weight to daily calories in four steps

Step one is the gap: 200 pounds minus 180 pounds is 20 pounds to lose. Step two is the burn. Resting metabolism comes from the Mifflin-St Jeor equation, which takes weight in kilograms, height in centimeters and age: 10 x kg + 6.25 x cm - 5 x age, plus 5 for men and minus 161 for women. The worked example, a 40 year old man at 200 pounds (90.72 kg) and 70 inches (177.8 cm), gives 10 x 90.72 + 6.25 x 177.8 - 5 x 40 + 5 = 1,823 calories. Step three multiplies by an activity factor to get the daily burn: 1,823 x 1.375 = 2,507 calories. Step four subtracts the deficit: at 1 pound a week the deficit is 500 calories, so the plan eats 2,507 - 500 = 2,007 calories a day.

The energy arithmetic behind step four is the one NHLBI uses: a 500 to 1,000 calorie daily reduction produces 1 to 2 pounds of loss a week, which works out to about 3,500 calories per pound. The same four steps for a 40 year old woman at 165 pounds and 65 inches give a 1,952 burn, so the same pace puts her at 1,452 calories a day, inside the band NHLBI describes for most women.

Pace: the CDC band and the calorie floors

CDC guidance (updated May 2025) describes a gradual, steady pace of about 1 to 2 pounds a week as the one people are more likely to keep off. The same page gives the first milestone: a 5 percent reduction, which for a 200 pound person is 10 pounds, and notes it can improve blood pressure, cholesterol and blood sugar. The pace you pick also fixes the intake floor problem, because the deficit and the diet size are two views of the same number.

NHLBI's Aim for a Healthy Weight guide pairs the 500 to 1,000 calorie cut with intake floors: plans of 1,000 to 1,200 calories help most women lose safely, and plans of 1,200 to 1,600 calories suit men and women who weigh 165 pounds or more or exercise regularly. Below 800 calories a day sits the very low calorie territory that NHLBI says should not be used routinely because it requires medical monitoring. The table shows how the pace drives the intake for the worked example.

The two flagged rows are where date driven planning lands: cutting from 2,507 to 1,007 calories to hit a date six weeks out asks for half the food a body needs at rest.

The same plan from two starting points

Two bodies make the point that the target intake scales with the burn. Take the man from the worked example: 200 pounds, goal 180, moderate activity, 1 pound a week. His numbers are a 2,507 burn, a 2,007 intake, a 20 week run, and a BMI that travels from 28.7 to 25.8. Take a 40 year old woman at 165 pounds with a 145 pound goal at the same pace: her burn is 1,952, her intake 1,452, her run also 20 weeks, and her BMI travels from 27.5 to 24.1. Same pace, same duration, completely different plates, because the 500 calorie deficit comes out of a different daily burn.

Both plans clear their reference floors with room to spare, which is what a 1 pound pace is supposed to do. Push either body to 2 pounds a week and the woman's intake drops to 952 calories, below her band, while the man sits at 1,507, still at his floor. The same pace is safe on one body and not the other, which is why the calculator recomputes the floor check from your own numbers rather than quoting a universal limit.

Dates, milestones and why the calendar slips

Twenty weeks at 1 pound a week means the plan that starts Monday, November 2, 2026 finishes Monday, March 22, 2027. The milestones fall on the same clock: 195 pounds at 5 weeks (December 7, 2026), 190 at 10 weeks (January 11, 2027), 185 at 15 weeks (February 15, 2027), 180 at 20 weeks. Writing the weights next to dates turns a distant goal into four checkpoints close enough to feel, and the calculator generates the same table from today's date whenever you run it.

Treat the date as an estimate with a known bias. The 3,500 calorie rule assumes the burn stays put while intake drops, and NIDDK's Body Weight Planner exists because real bodies adapt: as weight comes off, the burn falls, so late weeks lose less than early ones and the true finish date drifts later. Water swings of several pounds in a few days cut the other way and make week three look like a miracle. The fix is practical: recompute the plan every 10 pounds lost, and judge the pace by the four week trend rather than any single weigh in.

What the formula cannot see

The equation handles energy and nothing else. It does not know that fast deficits pull harder on muscle than slow ones. It does not know that the activity multiplier is the least reliable input on the page, because two people with the same desk job can differ by hundreds of calories in daily movement. It does not know about medicines, thyroid function, sleep or stress, all of which CDC lists among the factors that affect weight management. A formula that cannot see those things can still be useful, but it should be calibrated, not obeyed.

Calibration is simple. Run the calculator for two weeks, weigh in under the same conditions, and compare the actual loss with the promised loss. If the scale says 0.5 pounds where the math promised 1, your true burn is about 250 calories lower than the estimate, and the plan should be re-run with a lower activity factor or a smaller intake. NHLBI adds a medical boundary: anyone planning to lose more than 15 to 20 pounds, or considering a special formula diet, should be evaluated by a physician first. The calculator flags the pace; a clinician evaluates the person.

Mistakes that wreck the arithmetic

The most common error is feeding pounds into a metric formula. Mifflin-St Jeor takes kilograms and centimeters, so 200 pounds must enter as 90.72 kg and 70 inches as 177.8 cm; entering 200 as kilograms inflates the resting burn by more than 300 calories. The second is computing the burn once and riding it for six months: at the goal weight the same man burns 2,383 calories, 124 less than at the start, so a plan built on the original burn quietly overfeeds the finish line. Third is mixing the two deficit conventions, treating 500 as a weekly number and eating 4,000 calories on Sunday to compensate.

Two more are quieter. One is judging the pace by the first two weeks, when water loss makes every plan look like a miracle, then concluding the diet stopped working when the trend line catches up. The other is picking the goal weight from a formula rather than a conversation with a scale and a mirror; a goal that lands a BMI of 19 on a broad framed body is a goal built to fail. The calculator reports BMI at both ends precisely so the goal itself can be sanity checked before the eating starts.