Estimated Energy Requirement

Where the term comes from

Most calorie tools are named after what they do. This one is named after a term borrowed from formal nutrition science, and it is worth a minute of your time to know what it actually means, because "requirement" is a strong word.

Estimated Energy Requirement, or EER, comes from the Dietary Reference Intakes, the set of nutrition standards drawn up in the United States by what was then the Institute of Medicine. Most nutrients in that system get a recommended intake with a safety margin built in, deliberately set a bit above what an average person needs, so that almost everybody is covered. Energy does not work that way. You cannot add a safety margin to calories, because surplus energy does not get flushed away like surplus vitamin C. It gets stored.

So the EER was defined differently from the rest: it is the average energy intake predicted to keep a healthy person of your age, sex, size and activity level in energy balance. Not the most you can eat. Not a target to hit. The amount that, on average, keeps your weight where it is. A dietitian or a nutrition student meets this term in a textbook. If you have landed here from a course or a form that asked for your EER, that is the definition it wants.

The road this calculator takes

This is the honest bit, and we would rather say it plainly than let you assume.

The Dietary Reference Intakes publish their own equations for EER, and they look nothing like the ones most calculators use. The official adult versions run on height in metres and a physical activity coefficient of their own, something like this for men: EER = 662 − (9.53 × age) + PA × [(15.91 × weight in kg) + (539.6 × height in m)]. The activity coefficients in that system sit around 1.0 for sedentary up to about 1.48 for very active. That committee has since revisited the whole thing, and a new edition of the energy standards was published in 2023 with updated equations.

This tool does not run those equations. It takes the other well-travelled road to the same destination. First it works out your resting burn with 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

Then it multiplies that by an activity factor between 1.2 and 1.9 depending on what you selected. That is the same method our TDEE Calculator uses, and for a weight-stable adult, EER and total daily energy expenditure are describing the same quantity anyway.

So what should you take from this? That the number here is a sound estimate of your daily energy needs, arrived at by a widely used and well-validated route. But if you have been asked for an EER specifically in a clinical or academic setting, and the marker expects the Dietary Reference Intakes equations, this number will be in the same neighbourhood without being the identical figure. Different roads, same town. We would rather you knew which road we took.

A worked example

Take a 35 year old woman, 165 cm tall, 68 kg, who exercises moderately 3 to 5 times a week. Her resting burn first:

BMR = (10 × 68) + (6.25 × 165) − (5 × 35) − 161
BMR = 680 + 1031.25 − 175 − 161
BMR ≈ 1375 Calories/day

Then the moderate activity factor of 1.55:

EER = 1375 × 1.55 ≈ 2132 Calories/day

So roughly 2,132 calories a day should hold her weight steady. The tool also shows her resting figure underneath, and then a set of weekly targets, which is where things get more interesting.

The weekly targets, and the rule behind them

Alongside your EER, the tool lists what to eat to lose or gain roughly one or two pounds a week. Those come from subtracting or adding 500 and 1,000 calories a day, and there is a specific piece of arithmetic underneath.

It is the 3,500 calorie rule: the long-standing idea that a pound of body fat is worth about 3,500 calories, so a deficit of 500 a day, times seven days, equals one pound a week. The number traces back to a short paper by a doctor named Max Wishnofsky in 1958, and it has been repeated so often since that most people assume it is a law of physics.

It is not, and this is worth understanding before you plan your year around it. Kevin Hall, a researcher at the US National Institutes of Health, worked through what the rule actually predicts and showed where it breaks. The energy your body gives up per pound depends on how much fat you were carrying to begin with, so the rule fits reasonably well for people with a lot of body fat and overstates the deficit needed for leaner people. Worse, it assumes the maths keeps working forever. It does not. As you lose weight there is less of you to run, your daily burn falls, and the same 500 calorie cut buys you less and less. Plan a year of steady loss on this rule and reality will fall short of the arithmetic, not because you failed but because the rule was never built to run that long.

So read the weekly targets as a sensible starting point for the next few weeks, not a schedule. Recalculate as your weight changes.

Why the numbers stop falling

Try the two pound a week target on a smaller person and you will notice something: the number stops. Take the woman in the example above. Her EER is 2,132, so a 1,000 calorie cut would put her at 1,132 a day. The tool will not show that. It shows 1,200 instead, and holds there no matter what.

That floor is deliberate. This calculator will not present a weight-loss target below about 1,500 calories a day for men or 1,200 for women, because below that it stops being a diet and starts being a medical intervention.

The reasoning is straightforward. Food is the delivery system for everything your body needs, not just energy. Push intake low enough and you cannot fit in enough protein, vitamins and minerals no matter how carefully you choose, so the risk shifts from "this is difficult" to "this is harmful". Clinical guidance on rapid weight loss sits in the same territory: plans of roughly 1,200 to 1,500 calories a day for women and 1,500 to 1,800 for men are described as low-calorie diets and are meant to be followed with a healthcare provider watching. Anything under about 800 calories a day is a very low calorie diet, which belongs in a supervised programme with medical monitoring, not in a browser tab.

So if you hit the floor, the tool is not being unhelpful. It is telling you that the goal you picked is too aggressive for your body size, and that the honest answer is either a smaller weekly target or a conversation with a professional. Losing weight more slowly is not a failure. It is the version that works.

Where the estimate can be off

A few honest limits sit on top of everything above:

• It cannot see your body composition. Two people of the same age, height, weight and sex get the same number here, even if one carries far more muscle, which burns more at rest.
• The activity factor is the weak link. Most of the uncertainty in your result comes from that single dropdown choice, and most people rate themselves more active than they are.
• Health changes the requirement. Thyroid conditions, medications, pregnancy, breastfeeding, illness and recovery all move real energy needs in ways no height-and-weight formula can know about.
• Weight is asked for in kilograms here. If you think in pounds, divide by 2.2 before entering, or use our TDEE Calculator, which accepts either.

Use this as a starting figure to test against real life. If you are managing a health condition, or the targets here feel like a big change, take the number to a doctor or a registered dietitian rather than acting on it alone.

Questions people ask

Is EER the same as TDEE?

For a weight-stable adult, yes, they describe the same quantity: the calories that keep you where you are. EER is the term used in formal nutrition standards, TDEE is the term used in gyms and on the internet.

Does this use the official Dietary Reference Intakes equations?

No, and we would rather be upfront about it. It uses the Mifflin-St Jeor equation with an activity multiplier. The section above explains what the official equations look like and why the two land close but not identical.

Why will it not show me a lower number?

Because it holds a floor of roughly 1,500 calories for men and 1,200 for women. Below that, a target cannot reliably carry the nutrition you need, so the tool stops rather than hand you a figure that could do harm.

Should I eat exactly my EER?

Only if you want to stay the same weight, and even then treat it as a starting point rather than a rule. Watch what happens over a few weeks and adjust from what the scale actually tells you.

References

Where the figures come from. The definition of the Estimated Energy Requirement, and the official Dietary Reference Intakes equations quoted above, come from the Institute of Medicine's energy standards, summarised by the CDC, and were revisited by the National Academies in the 2023 edition. The resting equation this tool actually runs is Mifflin-St Jeor. The 3,500 calories per pound rule traces to Wishnofsky's 1958 paper, and the account of where it breaks down comes from Hall. The low-calorie diet figures behind the floor come from MedlinePlus, the patient information service of the US National Library of Medicine.

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. Gerrior S, Juan W, Basiotis P. An easy approach to calculating estimated energy requirements. Preventing Chronic Disease. 2006;3(4):A129. https://www.cdc.gov/pcd/issues/2006/oct/06_0034.htm
3. National Academies of Sciences, Engineering, and Medicine. Dietary Reference Intakes for Energy. Washington, DC: The National Academies Press; 2023. https://www.ncbi.nlm.nih.gov/books/NBK591020/
4. Wishnofsky M. Caloric equivalents of gained or lost weight. American Journal of Clinical Nutrition. 1958;6(5):542-546. https://doi.org/10.1093/ajcn/6.5.542
5. Hall KD. What is the required energy deficit per unit weight loss? International Journal of Obesity. 2008;32(3):573-576. https://doi.org/10.1038/sj.ijo.0803720
6. MedlinePlus. Diet for rapid weight loss. US National Library of Medicine. https://medlineplus.gov/ency/patientinstructions/000885.htm