// Basic Fitness Calculators

Calorie Deficit Calculator

Pick a weekly rate of loss and see the daily deficit it demands — and the calorie target that produces it.

Your details

Your result

Target calories
2,083kcal/day
Daily deficit
550kcal
Maintenance
2,633kcal/day
  • Don't drop below ~1,200 kcal (women) or ~1,500 kcal (men) without professional guidance.

Estimates are for general guidance only and are not medical advice. For a personalised plan, book a free guided tour at RPM Gym.

What your result means

This works backwards from the rate you choose. Half a kilogram of body fat is treated as roughly 7,700 kcal, so half a kilogram a week is 3,850 kcal spread across seven days: a deficit of 550 kcal a day. Change the rate and the deficit moves with it.

The three figures are meant to be read together: the deficit is the intervention, maintenance is what you're cutting from, and the target is what you actually eat. The same 550 kcal deficit is comfortable from a 3,000 kcal maintenance and severe from 1,800.

Choosing a faster rate doesn't make the loss more certain. It makes the daily gap larger, hunger higher and adherence worse, and the deficit you keep for three months always beats the one you abandon in three weeks.

How it is calculated

Energy-balance arithmetic on the 7,700 kcal-per-kilogram approximation

Maintenance = Mifflin-St Jeor BMR × activity factor Daily deficit = (weekly rate kg × 7,700) ÷ 7 Target calories = maintenance − daily deficit

What it assumes

  • One kilogram of body fat is treated as about 7,700 kcal. It's a widely used approximation, not a constant. The real figure varies with what proportion of the loss is fat rather than lean tissue and water.
  • The model assumes a constant deficit against a constant maintenance. In practice both drift downward as you lose weight.
  • Early weight loss is disproportionately water and glycogen, so week one usually overshoots this prediction and week four usually undershoots it.
  • The activity factor you select drives maintenance, and therefore the target. Over-selecting it is the most common reason a deficit fails to produce loss.

Units and rounding

  • Weight in kilograms, height in centimetres, age in years; rate in kilograms per week.
  • The deficit and target are kilocalories per day, rounded to whole numbers.
  • The tool won't stop you selecting an aggressive rate. Read the floor in the limitations before you do.

Worked example

A 35-year-old man, 95 kg, 180 cm, lightly active (1.375), targeting 0.5 kg per week.

  1. BMR = (10 × 95) + (6.25 × 180) − (5 × 35) + 5 = 1,905 kcal/day
  2. Maintenance = 1,905 × 1.375 = 2,619 kcal/day
  3. Daily deficit = (0.5 × 7,700) ÷ 7 = 3,850 ÷ 7 = 550 kcal/day
  4. Target = 2,619 − 550 = 2,069 kcal/day

A 550 kcal daily deficit and a 2,069 kcal target: a cut of about 21% from maintenance.

Limitations

  • Don't go below roughly 1,200 kcal a day as a woman or 1,500 as a man without professional supervision. Below those levels it becomes difficult to meet protein and micronutrient needs from food.
  • The 7,700 kcal-per-kilogram figure assumes the weight lost is fat. In an aggressive deficit, or without resistance training and adequate protein, a meaningful share of it is lean tissue instead.
  • Weight loss isn't linear and the scale is a poor daily instrument. Water, glycogen, salt, digestion and the menstrual cycle all move it by more than a day of deficit does.
  • Metabolic adaptation is real but usually smaller than assumed. The larger effect is that people move less and eat more than they record as a deficit runs on.
  • This is a general fitness tool. If you have a medical condition, take medication affecting appetite or metabolism, are pregnant or breastfeeding, or have a history of disordered eating, the right next step is a clinician rather than a calculator.

What to do next

  • Start at the gentler end. A 0.25–0.5 kg per week rate is where most people stay consistent, and consistency is what determines the twelve-week result.
  • Hold protein high while the deficit runs. It's the single most effective lever for keeping lean mass while losing weight.
  • Keep resistance training in the plan. A deficit without it reliably costs muscle alongside fat.
  • Judge progress on a weekly average taken under the same conditions, and give any change three weeks before reacting to it.
  • When you reach your goal, don't simply stop. Step back up towards maintenance deliberately. That transition is where most regain happens.

Sources

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CalorieMaintenance CaloriesProteinWeight Loss TimelineTDEEBMI
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// Frequently Asked

Questions, answered.

How big should my calorie deficit be?

For most people 500–550 kcal a day, which produces about half a kilogram of loss per week. Judge it as a percentage of your maintenance rather than an absolute: anything past about 25% below maintenance gets hard to sustain and starts costing lean mass.

How long does it take to lose 5 kg?

At 0.5 kg a week, about ten weeks of consistent adherence. At 0.25 kg a week, about twenty. The slower rate isn't worse. It's usually the one people actually complete.

Why am I in a deficit but not losing weight?

The two usual causes are an over-selected activity level, which inflates maintenance and shrinks the real deficit to nothing, and under-recorded intake. Before changing anything, check both against three weeks of scale data rather than one.

Is a 1,000 calorie deficit too aggressive?

For most people, yes. It targets a kilogram a week, which is achievable at higher body weights but increasingly costs lean tissue and adherence as you get leaner. It also pushes many people below the intake floor where nutrition becomes hard to meet.

Do I need a deficit every single day?

No. The weekly total is what matters. A higher day offset by lower ones produces the same result and is far easier to live around socially.

Will I lose muscle in a calorie deficit?

Some loss of lean tissue is normal, but how much is largely within your control. A moderate deficit, high protein and continued resistance training shift the balance strongly towards fat; a steep deficit without training does the opposite.

The deficit is arithmetic. Keeping your muscle through it is coaching.

Whether the weight you lose is fat is decided by how you train through the cut. Book a free guided tour at RPM Gym in Al Manhal.

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