The formula
How to calculate calorie calculator
Daily calorie needs start from BMR — the energy your body burns at complete rest — scaled up by an activity multiplier to get maintenance calories, then nudged up or down depending on whether the goal is to lose, gain or hold weight.
BMR uses the Mifflin-St Jeor equation. Multiplying it by the activity multiplier gives maintenance calories (also called TDEE). The goal dropdown then adds or subtracts a daily adjustment sized to the weekly rate of change built into whichever option is picked — "Lose 0.5 kg/week", for instance, carries both the direction and the size of the adjustment in one selection.
The calculator asks for:
- Gender
- Age (years)
- Height (cm)
- Weight (kg)
- Activity level
- Goal
No submit button: type and the answer moves. Your inputs end up in the link, so the page can be shared already filled in.
The order the fields are filled in makes no difference to the result — the calculator recomputes the whole formula from whatever is currently in every field, not step by step. That means it is safe to adjust one number, watch the result change, and adjust it back, without worrying about resetting anything first.
Why calorie calculator matters
The formula behind calorie calculator is standard and has not changed in decades; what changes is the situation it gets applied to. Two households can run the identical calculation and land on very different conclusions once their own numbers — income, rate, term, balance — are dropped in, which is why a generic textbook example is less useful than a calculator you can adjust to match your own circumstances.
This tends to come up when comparing two concrete alternatives — two lenders, two savings products, two ways of structuring the same decision — rather than in the abstract. Run both scenarios through the same calculator with the same assumptions and the comparison becomes fair, because the only thing changing between the two results is the number you are actually trying to test.
It is also worth being clear about what a single figure like this can and cannot settle on its own. It answers the specific question the formula was built to answer, and nothing more — a favourable calorie calculator result does not automatically mean a decision is a good one overall, since plenty of other factors that a formula cannot capture, from personal circumstances to how comfortable a commitment feels, usually matter just as much as the arithmetic. Use the number as one solid input among several rather than the whole of the decision.
A calculator like this one is often bookmarked and returned to repeatedly over months rather than used once, particularly for anything tied to an ongoing plan such as a mortgage, a savings goal or an investment being tracked. Because the figures live in the web address rather than only in memory, coming back to the same page with updated numbers is quicker than starting from a blank spreadsheet each time.
Worked example
Work through the defaults on this page:
- Gender: male
- Age: 30 years
- Height: 170 cm
- Weight: 70 kg
- Activity level: moderately_active
- Goal: maintain
That gives:
- BMR: 1,617.5 kcal/day
- Maintenance calories (TDEE): 2,507.1 kcal/day
- Daily calories for your goal: 2,507.1 kcal/day
- Weekly calories for your goal: 17,549.9 kcal/week
- Calories for selected goal: 2,507.1 kcal/day
- Estimated weekly weight change: 0 kg/week
These figures are only the calculator's own starting values, included so the working is visible rather than hidden inside the tool above. Replace them with your own numbers and the same arithmetic applies — nothing about the method changes, only the inputs feeding it.
Reading the result
Maintenance calories is the number that, eaten consistently, should hold weight steady. The daily-calories figure is what to actually eat for the selected goal — track weight for two to three weeks and adjust if the scale isn't moving at roughly the expected rate.
Where this goes wrong. The weekly-change adjustment is built on the rule of thumb that roughly 7,700 kcal equals 1 kg of body fat, so a 0.5 kg/week change needs about 3,850 kcal/week, or roughly 550 kcal/day — this calculator uses about 1,100 kcal/day per full kilogram of weekly change, scaled to whichever rate is picked. Aggressive rates (1 kg/week or more) push the daily adjustment high enough that it can be hard to sustain and risks losing muscle along with fat.
A useful check on any unfamiliar result is to compare it against a rough mental estimate first — round the inputs to convenient numbers and see whether the calculator's answer lands in roughly the same territory. A wildly different figure usually means one of the fields was entered in the wrong unit, most often a percentage typed as a whole number where a decimal was expected, or the reverse.
They're the same calculation shown two ways — "daily calories" is the number to eat each day, and "calories for selected goal" is the same figure framed around the goal you picked. Both come from maintenance calories plus the weekly-change adjustment.
Yes, when the goal is set to lose weight — a negative value means weight is expected to trend down by that amount each week. It reads as positive for weight gain and zero for maintenance.
The headline figure is bMR. With 30 years age, 170 cm height and 70 kg weight, that comes to 1,617.5 kcal/day. Change any field and the figure moves with it.
Whenever one of the underlying figures changes — a new interest rate, a different balance, an updated term — since the result only reflects what is currently in the fields. There is no need to keep a separate record of past results; the web address for a filled-in version already carries the figures used to produce it.
Not unless a tax rate or a fee is explicitly one of the inputs above. Where it is not, the figure shown is a gross calculation, and any tax due depends on your personal circumstances and current tax rules, which are worth checking separately.
The arithmetic itself is exact — the calculator applies the formula shown above precisely, with no rounding until the final figure is displayed. The uncertainty, where it exists, is entirely in the inputs: an estimated rate or an approximate balance carries that same approximation through to the result.