Calorie surplus calculator

Gaining weight can be just as hard as losing it. A gentle surplus on top of your everyday energy, added with nourishing foods, gives steady progress.

Your details

A gentle daily target

2,180

kcal a day

Your everyday energy1,883 kcal
Surplus+300 kcal
Likely pace0.3 kg (0.6 lb) a week
Protein to aim for52 g a day (UK reference amount, 0.75 g per kg)
Weeks to your goal, roughly17 (about 4 months)
Everyday energy at your goal weight1,945 kcal: eat about this to hold it there, and 2,245 kcal to keep gaining at the same pace
BMI at your goal27.3: above the healthy range, which is fine if the gain is muscle for sport; otherwise a lower goal may sit better

Your BMI is already 25 or more. If you are gaining for sport, pair this with strength training and keep an eye on your waist. Without strength training, more of any gain tends to be fat.

The working

Everyday energy plus a little

We take your TDEE and add the surplus you pick. At a TDEE of 1,883 kcal, a 300 kcal surplus gives 2,180 kcal a day (rounded). Using the 7,700 kcal per kilo rule, 300 a day is about 0.27 kg a week, or just over half a pound.

How to add it

Easy, nourishing extras

A milky drink or a glass of whole milk (about 130 kcal)
A handful of nuts (about 180 kcal)
Peanut butter on toast (about 250 kcal)
Full fat yogurt with granola
An extra snack between meals rather than huge portions

The NHS suggests gaining with healthy foods rather than lots of sugar and saturated fat, which can raise your risk of heart disease even if you are underweight.

Building muscle

Food plus lifting

For muscle rather than just weight, pair the surplus with strength training two or three times a week and enough protein (around 1.6 g per kg). Smaller surpluses mean more of the gain is muscle.

As you gain

Why the surplus shrinks

Your everyday energy rises as your weight goes up, so eating the same amount gives a smaller surplus over time and progress slows. That is the same effect Hall described for weight loss, run the other way.

For a 40 year old woman, 5 ft 5 in, 11 st, a bit active: Mifflin-St Jeor gives 1,369 kcal at rest and 1,883 kcal a day, so +300 is 2,180 kcal. At a goal of 11 st 10 lb (74.4 kg) the everyday energy is about 1,945 kcal, so holding the goal weight needs roughly that, and 2,245 keeps the same pace. 4.4 kg at 0.27 kg a week is about 17 weeks.

Protein: the UK reference amount is 0.75 g per kg a day. With strength training, a 2018 meta-analysis found gains levelled off around 1.6 g per kg, so we show 1.6 to 2.0 g per kg.

Read with care

What this cannot tell you

Unexplained weight lossIf you have lost weight without trying, see your GP first.
Eating difficultiesIf eating more feels hard or frightening, please get support.
Under 18sGrowing bodies have different needs; ask a GP or school nurse.

Questions

Common questions

How many extra calories to gain weight?

Around 300 to 500 kcal a day on top of maintenance for most people. That is roughly 0.25 to 0.5 kg a week.

How do I gain weight if I am not hungry?

Eat little and often, choose energy dense foods like nuts, cheese and milky drinks, and drink between meals rather than with them so you have room.

Why is my weight not going up?

Your activity might be higher than you think, or portions smaller. Add another 100 to 200 kcal and check again in two weeks.

Sources

Last checked 21 October 2026. Spotted something wrong? Tell us and we will fix it.

Underweight or losing weight?

If your BMI is under 18.5, or you have lost weight without meaning to, please see your GP. Beat has a free helpline on 0808 801 0677 if eating feels hard.