Weight loss wizard

What the three steps actually ask, and why

Step one takes your sex, age, height, weight and roughly how much you move. Those five inputs exist because the Mifflin-St Jeor equation needs four of them to estimate your resting metabolic rate, and the activity factor turns that resting figure into a whole-day figure. Nothing here is decorative: remove any one of them and the estimate gets materially worse.

Step two takes your goal weight and how fast you want to get there. The goal weight is not used to set a date. It is used to decide when the projection should stop, and to check that what you are aiming for sits inside the healthy weight range for your height. If it does not, the wizard says so rather than quietly planning it.

Step three is the output: what to eat, what that creates as a deficit, and what the deficit adds up to over time. There is no step four, and there is no account to create. The whole thing runs in your browser, and the only record of your numbers is the address bar, which you can copy or discard.

Without JavaScript the three steps collapse into one form and the server renders the plan from what you posted. The wizard is a convenience layered on top of a page that works without it, which is how every calculator on this site is built.

Where the daily burn estimate comes from

Your resting metabolic rate is estimated with Mifflin-St Jeor, published in 1990 and still the equation that performs best against measured values in the general adult population. It predicts the energy you would use lying still all day, which for most people is somewhere between sixty and seventy-five per cent of the daily total.

The activity factor does the rest, and it is by far the weakest link in the chain. The five bands run from 1.2 for a desk job with no exercise to 1.9 for a physical job or twice-daily training. They are rounded conventions rather than measurements, and two people who both describe themselves as moderately active can differ by several hundred calories a day.

That is why the whole estimate carries a band of roughly ten to fifteen per cent rather than a single confident number. A 2,900 calorie estimate could reasonably be 2,500 or 3,300. The plan is still worth making, because an estimate you then correct against two weeks of real weigh-ins beats having no starting point at all. What it is not is a measurement.

The rails this plan will not cross

Three limits are enforced in the calculation itself, not in the copy around it, so they apply whatever you select. The first is a rate cap at one per cent of bodyweight a week. Past that, the share of the loss that comes from muscle rather than fat rises sharply, and muscle is the tissue holding your daily burn up.

The second is a deficit floor at eighty per cent of your estimated daily burn. The third is an absolute floor of 1,500 calories for men and 1,200 for women, below which an ordinary mixed diet struggles to deliver enough protein, iron, calcium and the fat-soluble vitamins, regardless of how the calories are arranged.

If any of these change your plan, the page tells you which one and by how much. A calculator that silently clips your request and presents the result as though it were what you asked for is worse than one that refuses, because you never learn that a limit exists.

• Rate cap: one per cent of bodyweight a week, so a 95 kg person is held to 0.95 kg.
• Deficit floor: the target never drops below eighty per cent of estimated daily burn.
• Absolute floor: 1,500 kcal for men, 1,200 for women.
• Goal check: a goal below the healthy weight range for your height is refused, not planned.
• Under 18: the adult equations do not run at all, because a growing body has different needs.

How to read the day, week and month projections

Each row takes the same daily deficit and multiplies it out. One day of a 550 calorie deficit is 550 calories, or 2,301 kilojoules. Ninety days of it is 49,500 calories, or 207,108 kilojoules, which at the standard planning figure is about 6.4 kilograms. The arithmetic is simple and the table shows it openly.

What the table cannot do is predict you. It divides energy by 7,700 calories per kilogram, a figure Wishnofsky published in 1958 that assumes everything lost is fat and that your daily burn stays where it is today. Both assumptions decay. You get lighter, so you burn less. You move less without deciding to. Water shifts hide real fat loss for a fortnight at a time, and then release it all at once.

Kevin Hall and colleagues showed in 2011 that this rule systematically overpredicts as the months pass, which is why every row here is labelled a ceiling rather than a forecast. Treat the one-day and one-week rows as close to right, the one-month row as optimistic, and the three-month row as the best case if nothing drifts. Something always drifts.

The projection also stops. Once it reaches your goal weight, or the bottom of the healthy range for your height, the weight column holds there and the later rows stop moving. A projection that runs past a sensible endpoint is how a calculator ends up recommending a weight nobody should be aiming for.

Why protein decides what you actually lose

A deficit does not choose for you which tissue it takes. Protein intake and resistance training are the two things that push that choice towards fat. The wizard gives a range of roughly 1.6 to 2.2 grams per kilogram of bodyweight a day, which is the band the intervention literature supports for someone eating below maintenance and training.

That is well above the 0.8 grams per kilogram you will see quoted as the recommended intake. The lower figure is the amount that prevents deficiency in most healthy adults, which is a different question from the amount that preserves lean mass while you are underfed. Both numbers are correct; they answer different things.

The practical consequence is that protein is the one macronutrient worth planning before the others. Once it is set, carbohydrate and fat can be arranged around whatever is left in the budget, according to what you will actually eat. That is also why every meal at the end of this page leads on its protein figure.

When the plan stops working, and what to change

Expect the scale to stall at some point. The first question is always whether it has genuinely stalled or whether you are reading noise. Daily weight swings of a kilogram or more are ordinary, so a plateau means a flat four-week rolling average, not three disappointing mornings in a row.

If the average really is flat, the likeliest cause is not your metabolism. It is that the activity factor was too generous, or that intake has drifted upward in ways that do not feel like eating more. Restaurant portions, oil in the pan, drinks and the weekend all count, and the evidence on self-reported intake is that under-reporting is systematic rather than random.

Metabolic adaptation is real but smaller and slower than its reputation. Before blaming it, drop the activity band by one step, weigh what you eat for a week rather than estimating it, and see whether the average moves. If it does, the model was wrong, not your body.

The meals, and why these ones

A deficit does not fail at the planning stage. It fails on the evening you get home hungry with nothing ready, because at that point the easiest available option wins and the easiest available option is rarely the one that fits. The six meals at the end of the plan exist for that evening specifically.

Each one is under fifteen minutes, uses ingredients an ordinary supermarket stocks, and needs no technique you would have to learn. Several need no cooking at all. Every one carries thirty grams of protein or more in a single serve, because that is the number that makes the difference to what you lose.

The energy and protein figures are calculated from standard composition values for the raw ingredients and rounded. They are not laboratory measurements of the finished dish, and brands vary, so treat them as close enough to plan with rather than precise to the calorie. The protein figures survive rounding best, and they are the ones that matter here.

How it's calculated

Worked example: a man of 95 kg and 180 cm, aged 40, aiming for 85 kg

1. Resting rate, Mifflin-St Jeor for men: 10 × 95 = 950, plus 6.25 × 180 = 1,125, minus 5 × 40 = 200, plus 5. That is 950 + 1,125 − 200 + 5 = 1,880 kcal.
2. Daily burn at moderately active: 1,880 × 1.55 = 2,914 kcal.
3. Deficit for a steady 0.5 kg a week: 0.5 × 7,700 ÷ 7 = 550 kcal a day.
4. Check the rails: 0.5 kg is under the 0.95 kg rate cap for 95 kg; a 550 kcal deficit is under the 583 kcal that eighty per cent of 2,914 allows; and the target clears the 1,500 kcal floor. Nothing is capped.
5. Daily target: 2,914 − 550 = 2,364 kcal, which is 2,364 × 4.184 = 9,891 kJ. The deficit itself is 550 kcal, or 2,301 kJ.
6. One week: 550 × 7 = 3,850 kcal (16,108 kJ), which is 3,850 ÷ 7,700 = 0.5 kg.
7. One month, taken as 30 days: 550 × 30 = 16,500 kcal (69,036 kJ), which is 2.1 kg, leaving 92.9 kg.
8. Three months, 90 days: 550 × 90 = 49,500 kcal (207,108 kJ), which is 6.4 kg, leaving 88.6 kg. The 10 kg goal is not reached inside the table, and the page says so rather than inventing a date.
9. Read it as a ceiling. Real loss over ninety days usually lands below 6.4 kg, because the burn falls as the weight does.

Where this number is used in the real world

• Starting a cut and needing one number to eat to, rather than a vague instruction to eat less.
• Deciding whether a goal is realistic in the time you have, before committing to it.
• Converting between calories and kilojoules when the food labels where you live use the other unit.
• Understanding why a 10 kg goal is a season rather than a month, in arithmetic rather than opinion.
• Setting a protein target that protects muscle while the deficit runs.
• Having six meals decided in advance, so the hungry evening has an answer already.
• Re-planning after a stall, by correcting the activity band and seeing what the target becomes.

Frequently asked questions

Keep going

A single number rarely tells the whole story. Alongside the weight loss wizard result, the calorie deficit calculator, the TDEE calculator, the macros calculator, the protein calculator and the weight change % calculator each add a different angle on the same measurements. For the reasoning behind the numbers, read How many calories to eat, Adaptation and plateaus and How much protein.