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How to Calculate Calories for Weight Loss or Gain — TDEE Explained

Nutrition · 6 min read · Last updated September 2026

The energy balance principle

Body weight tracks energy balance: calories in versus calories out. Eat below expenditure and the body draws on stored energy; eat above it and surplus is stored. The calculation answers one question — what is your out?

Step 1: BMR (basal metabolic rate)

Step 2: TDEE (apply activity factor)

Step 3: apply the goal

• Fat loss: TDEE − 300 to 500 kcal (≈0.25–0.5 kg/week)
• Maintenance: TDEE
• Muscle gain: TDEE + 200 to 300 kcal (limiting fat gain)

Full worked example

Reading the scale correctly

• Week 1: much of early loss is water/glycogen — don't extrapolate.
• Weekly average vs daily weight: fluctuations of ±1–2 kg are normal from salt, carbs and hormones.
• Recheck monthly: as weight drops, TDEE drops — recalculate every 4–6 weeks.

Common mistakes

• Overestimating activity level — most people should start one tier lower than feels right.
• Counting exercise calories twice (activity factor + separate burn credits).
• Crash dieting below BMR for extended periods — adaptation makes regain likely.
• Ignoring protein and strength training, which protect muscle in a deficit.

Why the multiplier is the weakest link (and how to fix it)

Every number in the chain above is a measured regression — except the activity multiplier, which is a guess you make about yourself. The gap between tiers is enormous: for the worked example's BMR of 1,767.5, moving from 1.375 to 1.55 swings TDEE by 310 kcal/day — the entire intended deficit, created by one honest-vs-optimistic self-assessment. This is why "I'm eating less and not losing" so often traces to a multiplier chosen one tier too high, then exercise calories counted on top of it (double-counting — mistake #2 below).

The fix is calibration, not precision: treat the computed TDEE as a hypothesis, hold intake steady at it for 2–3 weeks while recording weekly average weight, then adjust by what happened. Weight held flat → that number was your TDEE, whatever the table said. Lost 0.4 kg/week → you were eating ~1,900 below true expenditure, and the deficit is bigger than intended. Two calibration cycles teach you more about your metabolism than any formula refinement — the calorie calculator gives the starting hypothesis, the record-keeping converts it to a fact.

Macros: turning calories into grams

Once the calorie target exists, macro targets are simple division — protein and carbs carry 4 kcal/g, fat 9 kcal/g. For an 80 kg lifter holding muscle on a 2,600 kcal target with a 30/40/30 split:

The split is a preference dials, not a law: protein anchored at 1.6–2.2 g/kg, fat above ~0.5 g/kg for hormones, and carbs filling the remainder is the standard, evidence-consistent approach. Precision beyond that earns nothing measurable — adherence does the work.

Worked example: Calorie Calculator at its default inputs

A worked example is only useful if you can reproduce it. The defaults on Calorie Calculator give exactly the figures in this section, with no rounding done by us.

Default inputs

Input	Default
Weight (kg)	70
Height (cm)	170
Age	30
Body Fat % (for Katch-McArdle)	15

Result: Daily Calories: 2507

The steps behind that answer

1. Step 1: Calculate BMR using mifflin formula = 1618 cal
2. Step 2: Apply activity factor 1.55
3. Step 3: TDEE = 1618 × 1.55 = 2507 cal/day
4. Step 4: To lose weight: 2006 cal/day

Weight (kg): half, as given, and half again

Hold every other field still and move only weight (kg).

Weight (kg): half, as given, and half again

Weight (kg)	Result
35	Daily Calories: 1965
70	Daily Calories: 2507
105	Daily Calories: 3050

If the rows barely differ, weight (kg) is not your lever — change a different input. If they swing widely, get that number right before trusting the total.

Related guides

• Macros
• Protein Need
• Health & Fitness Guides
• How to Calculate BMI

An estimate is a hypothesis, not a prescription

Predictive equations carry roughly a 10% error against measured expenditure, which is several hundred calories a day. Two people with identical inputs can differ by more than the deficit they are trying to create.

That is why the plan needs a test: eat the estimate for two to three weeks, weigh daily, and compare weekly averages. If weight is flat, the estimate is your maintenance, whatever the formula said.

Pick a rate you can hold

Roughly 7,700 kcal is stored in a kilogram of body fat, so a 500 kcal daily deficit predicts about 0.45 kg a week on paper. Real loss runs faster at first — glycogen and water leave with the first week of restriction — and slower later as the body gets smaller.

Half a percent to one percent of bodyweight per week is the range most people can sustain without losing muscle or abandoning the plan. Faster deficits mostly test willpower, and willpower has a budget.

The body adapts, and labels are approximate

A smaller body burns less at rest, and there is an additional adaptive component: measured expenditure often falls further than the weight change alone predicts. The same intake that produced loss in month one can produce a plateau in month four.

Logged intake is also usually under-reported, and packaged portions are allowed a margin of error on the label. If the scale disagrees with the arithmetic for three weeks, trust the scale and adjust the target.

FAQ

Do I need to hit macros exactly?

Calories drive weight change; protein adequacy (roughly 1.6–2.2 g/kg) helps preserve muscle. Carb/fat split is mostly preference within your calorie target.

Why did weight loss stop after a few weeks?

Commonly: TDEE fell with body weight, activity dropped unconsciously, or water retention masks fat loss. Recalculate, track weekly averages, and give it 2–3 more weeks before adjusting.

Does eating late at night matter?

Total daily intake matters far more than timing for weight. Meal timing can affect adherence and sleep — both worth optimizing, but not the core math.