Calorie Intake Calculator

From what you burn to what you eat

Most calorie calculators stop at what your body spends. This one goes one step further and turns that into a target: how much to actually eat, given what you are trying to do. That extra step is the whole point of the tool, and it is also where the responsibility sits, because a number you are told to eat carries more weight than a number describing what you burn.

So you entered your details and picked a goal, and the tool showed you a set of daily figures with your choice highlighted. This page explains where those come from, and it spends most of its time on the two things that matter most: how big a cut is sensible, and the point at which the tool stops cutting.

The formula this calculator uses

Three steps, and none of them are secret.

First, your resting burn, from the Mifflin-St Jeor equation:

Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161

Second, an activity multiplier, from 1.2 for little to no exercise up to 1.9 for heavy exercise 6 to 7 times a week. That gives your maintenance level, the calories that hold your weight steady.

Third, your goal is applied to that maintenance figure:

The tool asks for weight in kilograms and height in centimetres or inches, and it will not run for anyone under 18, because growing bodies have different energy needs and are not what this equation was built for.

A worked example

Take a 28 year old woman, 160 cm tall, 65 kg, doing light exercise 1 to 3 times a week. Her resting burn:

BMR = (10 × 65) + (6.25 × 160) − (5 × 28) − 161
BMR = 650 + 1000 − 140 − 161
BMR = 1349 Calories/day

With the light activity multiplier of 1.375, her maintenance comes to about 1,855 calories a day. From there the goals fan out:

Look at that fourth row. The arithmetic wanted to send her to about 1,113 calories a day. The tool refused, and showed her the floor instead. Both of those things deserve explaining, so they get a section each.

Why the goals are percentages, not fixed cuts

Plenty of calculators subtract a flat 500 calories from everyone and call it a diet. This one takes a percentage instead, and that choice is worth defending, because it is the more sensible of the two.

A fixed cut ignores the size of the person it is cutting from. Take 500 calories off a large, active man burning 3,200 a day and you have asked him to give up about 16 percent of his intake, which is a reasonable nudge. Take the same 500 off a small, sedentary woman burning 1,600 and you have asked for 31 percent, which is a different proposition entirely, from someone with far less room to give. Same number, wildly different demand.

Scaling the cut to the person keeps the difficulty roughly constant. The 10 percent option is a gentle trim that most people barely notice. The 20 percent option is a real diet that most people will feel. And 40 percent, well, that has its own section, immediately below.

About that 40 percent option

It is in the dropdown, so it is only fair to be straight about what it is. A 40 percent cut is an aggressive deficit, and for most people it is more than they need and more than they should attempt without support.

Here is the context. Mainstream clinical guidance for weight loss lands around a deficit of 500 to 750 calories a day, which for most adults works out somewhere near 15 to 25 percent below maintenance, and produces steady loss of roughly half a kilogram a week. Our 10 and 20 percent options sit comfortably inside that range. The 40 percent option sits well outside it.

Why does that matter, when faster sounds better? Three reasons worth knowing before you pick it.

• You lose more than fat. A steep deficit strips muscle alongside fat, and muscle is the tissue that keeps your resting burn up. You end up lighter and with a slower engine, which is the opposite of what you wanted.
• The nutrition stops fitting. Below a certain intake there is not enough food to carry the protein, vitamins and minerals you need, no matter how carefully you shop.
• It usually does not stick. People who lose weight very quickly are more likely to regain it than people who lose slowly, because rapid loss is a bigger stress on the body and provokes a stronger hormonal pushback.

So the honest advice from a page whose own tool offers the option: use 10 or 20 percent. If your situation genuinely calls for something more aggressive, that is a conversation with a doctor or a registered dietitian, not a dropdown.

The floor you might hit

Pick a goal that would send you too low and the tool does not comply. It shows about 1,500 calories for men or 1,200 for women, labelled as the guideline floor, and holds there.

That floor is not arbitrary. Food is the delivery system for everything your body needs, not just energy, and push intake far enough down and the nutrition simply cannot fit. Clinical guidance treats plans of roughly 1,200 to 1,500 calories a day for women and 1,500 to 1,800 for men as low-calorie diets, meant to be run with a healthcare provider watching. Below about 800 calories a day you are into very low calorie diet territory, which belongs to supervised medical programmes with monitoring, a time limit and a plan for coming back off it.

So when the number stops moving, the tool is telling you something useful: the goal you selected is too aggressive for your body size. The answer is not to find a calculator that will give you the lower number. It is to pick a gentler goal, or to talk to someone qualified.

Where the estimate can be off, and who should skip it

This is a general-purpose tool built on population averages, and there are people it is not built for:

• Anyone under 18. The tool will not run, because growing bodies need more than this equation knows how to give.
• Pregnancy and breastfeeding. Energy needs rise, and a maintenance-minus-something figure does not apply. Ask a professional.
• Anyone with a health condition that touches metabolism or nutrition, including thyroid conditions, diabetes, and anything requiring medication that affects appetite or weight.
• Anyone with a history of disordered eating. If counting calories has been a difficult place for you before, a number on a screen is not neutral. Please talk to someone rather than start here.

Beyond that, the usual limits apply. The equation cannot see your body composition, the activity multiplier is the roughest part of the whole calculation, and if you have recently lost weight your true maintenance is likely lower than predicted, as our Maintenance Calorie Calculator explains. Treat the result as a starting point to test against the scale over a few weeks, not a rule to obey.

Questions people ask

Which goal should I pick?

For most people, mild or moderate loss, which is the 10 or 20 percent option. Those match mainstream clinical advice, keep more of your muscle, and are far easier to stay with, which is what actually decides the outcome.

Why does it say guideline floor instead of a number?

Because your chosen goal would have taken you below the floor of roughly 1,500 calories for men or 1,200 for women. Below that the target cannot reliably carry the nutrition you need, so the tool stops rather than hand you a figure that could do harm.

Can I eat below my BMR?

It happens on any meaningful diet, and it is not automatically dangerous, since your body makes up the difference from stored energy. What matters is how far below your maintenance you are and for how long, which is exactly what the percentage options and the floor are managing.

Why is the gain option a flat 500 rather than a percentage?

That is simply how this tool is built: losses scale to your size, the gain adds a fixed 500 calories. For most people a surplus of that size supports muscle gain without much fat coming along, though a smaller surplus of 250 to 300 is often the leaner choice if you are in no hurry.

I am eating the target and not losing weight. What now?

Usually one of three things: the activity level you picked is optimistic, your intake is higher than you think, or your maintenance has drifted down. Drop by a hundred calories or so, give it a fortnight, and watch the trend rather than any single day's weight.

References

Where the figures come from. The resting equation this tool runs is Mifflin-St Jeor, published in the American Journal of Clinical Nutrition, and the finding that it is the most accurate of the common equations comes from a systematic review by the Academy of Nutrition and Dietetics. The low-calorie diet figures behind the floor, and the point that rapid loss is more likely to be regained, come from MedlinePlus, the patient information service of the US National Library of Medicine. The clinical deficit range of 500 to 750 calories a day comes from the American College of Cardiology, American Heart Association and Obesity Society guideline on managing overweight and obesity in adults.

1. Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition. 1990;51(2):241-247. https://doi.org/10.1093/ajcn/51.2.241
2. MedlinePlus. Diet for rapid weight loss. US National Library of Medicine. https://medlineplus.gov/ency/patientinstructions/000885.htm
3. Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association. 2005;105(5):775-789. https://doi.org/10.1016/j.jada.2005.02.005