Calorie & Deficit Calculator
Estimate your BMR (resting burn), adjust for activity to get TDEE (maintenance calories), and set an optional deficit or surplus to hit your goals. See steps, a mini bar chart, and a deficit gauge for quick insight.
Background
We use the Mifflin–St Jeor equation for BMR (default). If you provide body fat %, we switch to Katch–McArdle (LBM-based). Your TDEE = BMR × activity factor. Target intake applies a chosen weekly pace to compute an energy delta (≈7700 kcal/kg or 3500 kcal/lb heuristic).
How this calculator works
- BMR (resting): Mifflin–St Jeor uses age, sex, height, weight. If body fat % is provided (and toggled), we switch to Katch–McArdle using lean mass.
- TDEE (maintenance): Multiply BMR by your activity factor.
- Goal target: Convert weekly pace → daily kcal change (≈3500 kcal/lb or 7700 kcal/kg) and adjust TDEE.
- Safety note: We warn if the requested deficit/surplus exceeds ~35% of TDEE.
Formula & Equations Used
Mifflin–St Jeor (kcal/day)
Male: BMR = 10·mass(kg) + 6.25·height(cm) − 5·age + 5
Female: BMR = 10·mass(kg) + 6.25·height(cm) − 5·age − 161
Katch–McArdle (kcal/day)
BMR = 370 + 21.6·LBM(kg), where LBM = mass·(1 − body fat %)
TDEE: BMR × activity factor
Pace → kcal/day: Δ ≈ 7700·pace(kg/wk)/7 or 3500·pace(lb/wk)/7
Activity Level Reference
These are the exact multipliers this calculator applies to BMR to get TDEE.
| Activity level | Multiplier | Typical pattern |
|---|---|---|
| Sedentary | ×1.2 | Little or no exercise, desk job |
| Light | ×1.375 | Light exercise 1–3 days/week |
| Moderate | ×1.55 | Moderate exercise 3–5 days/week |
| Very active | ×1.725 | Hard exercise 6–7 days/week |
| Extra active | ×1.9 | Very hard training or a physical job, plus exercise |
Deficit or Surplus vs. Weekly Weight Change
Using the same ≈7700 kcal/kg (≈3500 kcal/lb) heuristic this calculator uses internally.
| Daily change | Per week (kcal) | Expected weekly change |
|---|---|---|
| ±250 kcal/day | 1,750 kcal/week | ≈0.23 kg (≈0.5 lb) |
| ±500 kcal/day | 3,500 kcal/week | ≈0.45 kg (≈1 lb) |
| ±750 kcal/day | 5,250 kcal/week | ≈0.68 kg (≈1.5 lb) |
| ±1,000 kcal/day | 7,000 kcal/week | ≈0.91 kg (≈2 lb) |
This is a simplified, widely-used estimate. Real-world weight change also depends on water retention, glycogen stores, and individual metabolic variation.
Example Problem & Step-by-Step Solution
Example 1 — Male, 22 y, 180 cm, 75 kg, moderate, −0.5 kg/week
BMR (MSJ) ≈ 10·75 + 6.25·180 − 5·22 + 5 = 1,770 kcal/day. Activity 1.55 → TDEE ≈ 2,744 kcal/day. Weekly pace −0.5 kg → ≈ 7700·0.5/7 ≈ 550 kcal/day deficit → Target ≈ 2,194 kcal/day.
Example 2 — Female, 21 y, 165 cm, 62 kg, light, maintenance
BMR (MSJ) ≈ 10·62 + 6.25·165 − 5·21 − 161 = 1,385 kcal/day. Activity 1.375 → TDEE ≈ 1,905 kcal/day (target = maintenance).
Example 3 — Male, 28 y, 5'10", 180 lb, moderate, −1 lb/week
Convert: 180 lb ≈ 81.65 kg; 5'10" ≈ 177.8 cm. BMR (MSJ) ≈ 10·81.65 + 6.25·177.8 − 5·28 + 5 = 1,793 kcal/day. TDEE ≈ 1,793×1.55 = 2,779 kcal/day. Pace −1 lb/wk → 3500/7 = 500 kcal/day deficit → Target ≈ 2,279 kcal/day.
Example 4 — Female, 30 y, 5'5", 140 lb, sedentary, +0.5 lb/week
Convert: 140 lb ≈ 63.5 kg; 5'5" ≈ 165.1 cm. BMR (MSJ) ≈ 10·63.5 + 6.25·165.1 − 5·30 − 161 = 1,356 kcal/day. TDEE ≈ 1,356×1.2 = 1,627 kcal/day. Pace +0.5 lb/wk → 3500·0.5/7 = 250 kcal/day surplus → Target ≈ 1,877 kcal/day.
Frequently Asked Questions
Q: Which BMR equation do you use?
Mifflin–St Jeor by default; if body fat % is supplied and enabled, we use Katch–McArdle.
Q: How accurate are calorie estimates?
They are estimates. Individual variation (NEAT, thermogenesis, measurement error) can shift real needs by 5–15% or more.
Q: Is a 1000 kcal/day deficit safe?
Large deficits can be risky. We flag anything beyond ~35% of TDEE. Consult a clinician for personalized guidance.
Q: What is TDEE and why does it matter?
TDEE (Total Daily Energy Expenditure) is roughly how many calories you burn in a day, including daily movement and exercise — your BMR multiplied by an activity factor. It's the number that matters most: eat around your TDEE to maintain weight, below it to lose, above it to gain.
Q: How many calories should I cut to lose 1 pound a week?
About 500 kcal/day (≈3,500 kcal/week), using the common ≈3,500 kcal per pound heuristic. In metric terms, roughly 550 kcal/day gets you close to 0.5 kg/week. This calculator uses 500 kcal/day as its default deficit when no pace is specified.
Q: Should I eat back the calories I burn exercising?
Usually no, if you've already selected an activity level that reflects your typical exercise — that activity multiplier already accounts for it inside your TDEE. Adding exercise calories on top of an activity-adjusted TDEE tends to double-count them and can undermine a deficit.
Q: Why do different calorie calculators give me different numbers?
Small differences are normal. Calculators can use different BMR equations (Mifflin–St Jeor vs. Katch–McArdle vs. others), different activity-level definitions, and different rounding. A 5–10% spread between reputable calculators is typical and doesn't mean either one is "wrong."
Q: When should I use Katch–McArdle instead of Mifflin–St Jeor?
Katch–McArdle (which this calculator offers when you enter body fat %) tends to be more accurate for people who are leaner or more muscular than average, since it's based on lean body mass rather than total weight. If you don't know your body fat % — or aren't confident in the number — Mifflin–St Jeor is the better general-purpose default.
Q: I'm eating my target calories but not losing weight — what's going on?
This is common and usually comes down to a few things: calorie tracking is often less precise than it feels (portion sizes, hidden oils, drinks), water retention can mask fat loss for a week or two, and individual metabolic variation means the real number can be 5–15% off from any estimate. Give it 2–3 consistent weeks before concluding the target itself needs adjusting.
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