How Many Calories to Gain Weight: Working Out Your Number

Written by James Frost, founder of Flaming Phoenix. Updated October 2026.

Quick answer: To gain weight, eat 300 to 500 calories a day above your maintenance, the intake that keeps your weight steady. Using NHS averages (2,000 calories for women, 2,500 for men), that means about 2,300 to 2,500 a day for women and 2,800 to 3,000 for men. A pound takes roughly 3,500 extra calories; a kilo, about 7,700.

This page is about the numbers: finding your maintenance, choosing the surplus, what 3,500 per pound really means, and how to correct your figure once the scales start giving you feedback. For what to actually eat, see my guide to how to gain weight. If you just want your number, the weight gain calculator works it out from your age, height, weight and activity.

How many calories do you need to gain weight?

You need your maintenance calories plus about 300 to 500 a day, the range the NHS suggests for adults who want to gain weight gradually. Maintenance depends mostly on your size, age, sex and how active you are, so the total varies a lot from one person to the next.

Here is the working for two people, using the Mifflin-St Jeor equation that our calculator uses and a 1.55 multiplier for training three to five times a week:

• A 25-year-old man, 178cm and 65kg. Resting rate: 10 × 65, plus 6.25 × 178, minus 5 × 25, plus 5 = about 1,640 calories. Times 1.55 = about 2,550 maintenance. Target to gain: 2,850 to 3,050 a day.
• A 25-year-old woman, 165cm and 52kg. Resting rate: 10 × 52, plus 6.25 × 165, minus 5 × 25, minus 161 = about 1,265 calories. Times 1.55 = about 1,950 maintenance. Target to gain: 2,250 to 2,450 a day.

Both land close to the NHS averages of 2,500 calories a day for a man and 2,000 for a woman, which makes those averages a fair sense check. Someone taller, heavier or in a physical job can need several hundred more.

How many calories above maintenance should you eat to gain weight?

For steady weight gain, eat 300 to 500 calories above maintenance, which adds roughly 0.25 to 0.5kg (about half a pound to a pound) a week. That is enough to see progress within a month and small enough to keep up.

Which end to pick depends on you. I would start at 300 if you are smaller, sit for most of the day, or want as little of the gain as possible to be fat. Start at 500 if you train hard, have a physical job, or have already tried a smaller increase without the scale moving. If you are lifting to build muscle, the bulking calculator sets the surplus around your training.

A bigger surplus of 700 to 1,000 a day adds weight faster, but more of it comes on as fat and it is much harder to sustain. For most people the moderate surplus is the better long-term choice. The behaviour side of holding a surplus every day, which is what makes the numbers work, is covered in my calorie surplus guide.

How many calories does it take to gain a pound?

It takes roughly 3,500 extra calories to gain a pound (0.45kg), or about 7,700 for a kilo. That is the long-standing rule of thumb, and Mayo Clinic describes it as a figure from past research that does not hold for everyone.

The arithmetic for common goals:

• A pound a week: 3,500 ÷ 7 = 500 extra calories a day.
• Half a kilo a week: 3,850 ÷ 7 = 550 a day.
• A pound a month: 3,500 ÷ 30 = about 120 a day.
• A kilo a month: 7,700 ÷ 30 = about 260 a day.
• Ten pounds: 35,000 extra calories in total. In two weeks that would mean 2,500 a day on top of maintenance, which few people can eat for long; at 500 a day it takes about ten weeks.

Treat the rule as a rough guide, for two reasons.

• It describes fat. Lean tissue is mostly water and protein and holds far fewer calories per kilo, a point Kevin Hall of the US National Institutes of Health made in a 2008 paper on the rule. When part of your gain is muscle, water and stored carbohydrate, the scale can move faster than 3,500 per pound predicts, especially in the first few weeks.
• Your maintenance rises as you gain. A heavier body burns more, so the same intake gives a smaller surplus over time. Hall's later modelling in The Lancet found that body weight responds slowly to a lasting change in intake, taking about a year to get halfway to its new level. In practice, a surplus that works in month one can stall by month three, so re-check your number after every 2 to 3kg gained.

How to work out your maintenance calories

Estimate maintenance with an equation, then confirm it by tracking what you eat for a fortnight while your weight holds steady; the measured figure beats any formula.

The estimate. Mifflin-St Jeor is the usual choice: a 2005 systematic review for the American Dietetic Association found it predicted resting metabolic rate within 10% of the measured figure in more people than the other common equations. Multiply the result by an activity factor, from 1.2 if you mostly sit to 1.9 if you have a physical job and train hard, and you have a starting maintenance figure. The calculator does this for you. A rougher shortcut is your bodyweight in pounds times 14 to 16, but it tends to run low for lighter, active people, which describes a lot of people trying to gain.

The measurement. Eat as you normally would for a week or two, track it honestly, and weigh yourself a few times a week. Whatever intake keeps your weight roughly steady is your real maintenance, measured rather than guessed. You do not have to track forever, just long enough to find your number. Add 300 to 500 to it and that is your target.

How accurate is your calorie number?

Your number is an estimate, and even a good one can be a couple of hundred calories out: 10% of a 2,500-calorie day is 250 calories either way. An equation cannot see how much you fidget, how hard you train or how your particular metabolism runs, so two people of the same age, height and weight can have maintenance figures hundreds of calories apart.

So treat any number, including the ones above, as a starting point to test. The real measurement is what the scales do over two to three weeks.

How to adjust your number

Give any target two to three weeks before judging it, because weight bounces around daily with water and food in the gut, and a single weigh-in tells you very little. Weigh once a week, on the same day and before breakfast, and look at the trend.

If your weight has not moved after three weeks, add another 200 to 300 calories a day and reassess. If it is climbing faster than about 0.5kg a week, ease back by a similar amount. Every 2 to 3kg, re-run the calculator with your new weight, because your maintenance will have risen with it. As a worked example: start at 2,550 maintenance and a 2,850 target, gain steadily for six weeks, then stall. The next step is 3,050 to 3,150 a day, not giving up.

How do you hit a higher calorie target every day?

Add a few fixed, known amounts to the day, so the surplus does not depend on guessing portion sizes or remembering to eat more at every meal.

A 250ml glass of whole milk is about 160 calories, a 30g handful of nuts about 180, and a tablespoon of olive oil about 120, so any two of them cover a 300-calorie surplus. Figures are approximate for standard UK portions.

A labelled bar works the same way. Each of our Phoenix Bars has up to 557 calories in only 120g, a fixed figure you can add without weighing anything. They are vegan and gluten-free, need no preparation, and can be stirred into milk as porridge. You can see the range of high calorie bars for weight gain on our homepage, and easy ways to eat more calories has more ideas. Once you know your target, the 3,000 calorie meal plan shows a whole day at roughly that level.

Frequently asked questions

How many calories should I eat a day?

The NHS uses 2,000 calories a day for an average woman and 2,500 for an average man as a general guide to keeping weight steady. Your own figure depends on your age, height, weight and activity. To gain weight, add 300 to 500 to your maintenance; to stay the same, eat at it.

How many calories should a man eat to gain weight?

About 2,800 to 3,000 a day for an average man: the NHS figure of 2,500 plus a 300 to 500 surplus. Taller, heavier or very active men need more. A 25-year-old who is 185cm, weighs 75kg and trains hard most days works out at around 3,400 to 3,600 using Mifflin-St Jeor.

How many calories should I eat to gain weight fast?

A surplus of 700 to 1,000 calories a day above maintenance gains weight faster, roughly 0.6 to 0.9kg a week by the 7,700-per-kilo rule, but more of it comes on as body fat and it is harder to keep up. For most people a steadier 300 to 500 is the better approach; my guide to gaining weight fast covers the trade-offs.

Can you build muscle at maintenance calories?

Some people can, mostly beginners and people returning to training, but progress is slow and body weight barely changes. If the goal is to weigh more, you need a surplus. 300 to 500 calories a day with strength training two or three times a week is the usual starting point, with protein set using the protein calculator for weight gain.

How accurate are calorie counts on food labels?

Close, but not exact. Cleveland Clinic notes that label figures can be out by as much as 20%, and portions served at home vary even more. That is one more reason to let a three-week weight trend, rather than the arithmetic, decide whether you need to eat more.

Do I need a calorie calculator to gain weight?

No. A calculator gives a starting estimate, but it cannot know your exact needs. You can get a similar starting point from the NHS averages, and the real adjustment comes from tracking your weight over a few weeks and changing your intake based on the result.

Related guides

For the method behind a surplus, see how to eat in a calorie surplus and how to gain weight. If your number looks impossibly high, my guide to gaining weight with a fast metabolism is for you. For hitting the number, see easy ways to eat more calories and the 3,000 calorie meal plan, and for the porridge method, how to use Phoenix Bars.

If you have a question about your number, email me at jfrost@flaming-phoenix.co.uk. I answer every email myself.

Sources: NHS, Healthy ways to gain weight; NHS, Understanding calories; Mayo Clinic, Counting calories; Mifflin and others, American Journal of Clinical Nutrition, 1990; Frankenfield and others, Journal of the American Dietetic Association, 2005; Hall, International Journal of Obesity, 2008; Hall and others, The Lancet, 2011; Cleveland Clinic, How many calories are in a pound.