Weight Gain Calculator

weekly gain = daily surplus × 7 ÷ 7,700 · days = kilograms to gain ÷ weekly gain × 7

current

The weight you are at now, in kilograms (kg)

target

The weight you are aiming for, in kilograms (kg)

surplus

The extra calories you add each day, on top of what you already eat (kcal)

7,700

The energy in a kilogram of body mass, the same constant the weight loss page uses in the other direction (kcal)

Use it when you want to put on weight on purpose — after illness, during a strength programme, or because you have always been light — and you want to know whether the plan you have in mind is a month or a year. It also answers the reverse question, which is often the useful one: if you keep eating the way you do now, how long until you reach that weight. It is not a pregnancy weight gain calculator and takes no account of one; it does not prescribe a diet, and it cannot tell you how much of the gain will be muscle rather than fat, which depends on training and protein rather than on the size of the surplus.

1. 60 kg to 70 kg, eating 550 extra calories a day

   1. Weekly gain: 550 × 7 ÷ 7,700 = 0.5 kg a week
   2. Kilograms to gain: 70 − 60 = 10 kg
   3. Days: 10 ÷ 0.5 × 7 = 140 days, which is 20 weeks
   4. Date: 140 days after the day of the calculation
   5. Total extra energy: 550 × 140 = 77,000 kilocalories

   The total is the number worth sitting with. 77,000 kilocalories is 10 × 7,700, the arithmetic checking itself — and it is roughly five weeks of food for an average adult, spread across more than four months.

2. 60 kg to 70 kg, eating 1,650 extra calories a day

   1. Weekly gain: 1,650 × 7 ÷ 7,700 = 1.5 kg a week
   2. Days: 10 ÷ 1.5 × 7 = 46.7, rounded to 47 whole days
   3. Weeks: 47 ÷ 7 = 6.7
   4. Total extra energy: 1,650 × 47 = 77,550 kilocalories

   Tripling the surplus cuts the time to about a third, and the total barely moves — the energy needed is set by the kilograms, not by the speed. What does change is where the weight comes from: a surplus this large is well past what muscle can use.

The 7,700 figure is an approximation, and a long-standing one: it treats a kilogram of body mass as if it were all fat and as if the body simply banked the difference, when in reality a large surplus raises the energy you burn and partitions some of the extra into tissue that costs more to build than it stores. Part of any gain is lean tissue and part is fat, and this page cannot tell you the split — that depends on whether you are training, how much protein you eat, and where you started. A surplus of a thousand calories a day is not a faster version of a surplus of five hundred; past a few hundred calories the extra is increasingly stored as fat, and the page will still print a shorter timeline for it. The date is arithmetic, not a promise: it assumes the surplus happens every single day, which no plan survives intact. And it assumes weight gain is what you want — for anyone with a history of an eating disorder, or gaining weight for a medical reason, a clinician should set the target and the rate rather than a calculator.

How many calories a day do I need to gain weight?

Start with a few hundred on top of what you already eat, not a thousand. At 550 extra calories a day the arithmetic gives half a kilogram a week, which is a rate most people can eat consistently and which leaves room for training to direct some of the gain into muscle. The number is a starting point to be adjusted against the scale after three or four weeks, not a target set once: the larger the surplus, the higher the share of it that ends up as fat.

Is this the same as a pregnancy weight gain calculator?

No, and the two have almost nothing in common. Pregnancy weight gain is not an energy-balance question at all — it has published ranges indexed by pre-pregnancy BMI, it moves on a schedule set by the week of pregnancy, and the recommendations come from obstetric bodies rather than from a calorie constant. If you are pregnant, use the pregnancy page; this one takes no account of pregnancy and would give you a number that means nothing.

How much of the gain will be muscle?

That is not something this page can answer, and no calculator can. The surplus sets the amount of tissue available; what that tissue becomes depends on whether you are lifting, how much protein you eat, how much you sleep, and how far you are from your genetic ceiling. A common approach is a small surplus with heavy training and enough protein, checking the scale and the waistline every few weeks — if the waist is growing much faster than the arms, the surplus is bigger than the training can use.

Why does tripling the surplus not triple the result?

It does shorten the timeline, and the page will show it, but the relationship is not honest at the top end. A large surplus raises your total daily energy expenditure, so part of the extra is simply burned; and the body has a limited rate at which it can build lean tissue, so the remainder goes to fat. The total energy column makes the same point from the other side: the kilocalories needed are fixed by the kilograms, so eating faster changes the schedule and not the bill.

What if I want to lose weight instead?

Enter a target below your current weight and the page still works: the weekly and total figures come back negative, which is the same sign convention the weight loss calculator uses. That is fine for a quick estimate, and if losing is the actual goal the weight loss page is the better tool — it takes a pace rather than a calorie number and it applies the published guidance on how fast is sensible, which this page deliberately does not do in the gaining direction.

• Caloric equivalents of gained or lost weight — Wishnofsky M — American Journal of Clinical Nutrition, 1958
• Losing weight — healthy weight growth — US Centers for Disease Control and Prevention