How to Calculate Your Calorie Deficit (Step-by-Step)

Q: How do I calculate my calorie deficit manually?

Step 1: calculate BMR (Men: 10×kg + 6.25×cm − 5×age + 5; Women: same −161). Step 2: multiply BMR by activity factor (1.2–1.9) to get TDEE. Step 3: subtract 500 kcal from TDEE for your fat loss daily target.

Q: How often should I recalculate my calorie deficit?

Recalculate every 4–6 kg of weight lost. As body weight decreases, TDEE decreases, and the same calorie intake creates a progressively smaller deficit. Failing to update is the most common reason fat loss slows and plateaus occur.

Calculating your calorie deficit manually takes three steps: find your BMR, multiply by your activity factor to get TDEE, then subtract your target deficit to arrive at your daily calorie intake goal. This guide walks through each step in full with a real worked example, explains how to choose the right deficit size for your goals, and shows you when to recalculate as your weight changes.

By the FitCalcHub Editorial Team — Updated August 2026 — 8 min read

Step 1 — Calculate Your BMR

Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest. It is the foundation of every calorie calculation. The most validated equation for healthy adults is the Mifflin-St Jeor equation:

Men: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
Women: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161

Worked example — 28-year-old woman, 72 kg, 168 cm:
BMR = (10 × 72) + (6.25 × 168) − (5 × 28) − 161
BMR = 720 + 1,050 − 140 − 161 = 1,469 kcal/day

Based on: Mifflin MD, St Jeor ST, et al. "A new predictive equation for resting energy expenditure in healthy individuals." Am J Clin Nutr. 1990;51(2):241–247. PubMed ↗

Step 2 — Multiply by Your Activity Factor (TDEE)

Multiply your BMR by the activity factor that best matches your average daily lifestyle — not just your gym sessions, but all movement throughout the day:

Activity level	Description	Multiplier
Sedentary	Desk job, little to no exercise	× 1.2
Lightly active	Light exercise 1–3 days/week	× 1.375
Moderately active	Moderate exercise 3–5 days/week	× 1.55
Very active	Hard exercise 6–7 days/week	× 1.725
Extremely active	Physical job + hard training daily	× 1.9

Continuing the example — our 28-year-old woman exercises 3–4 days/week (moderately active):
TDEE = 1,469 × 1.55 = 2,277 kcal/day

This is her maintenance intake — the amount she needs to eat to keep her weight stable. Use our TDEE Calculator to calculate your personal figure, or use the BMR Calculator to get your resting rate first.

Step 3 — Subtract Your Target Deficit

Subtract 250–500 kcal from your TDEE to create your fat loss calorie target. The deficit size determines how fast you lose:

Deficit	Daily target (example)	Expected loss/week	Best for
−250 kcal/day	2,027 kcal	~0.25 kg	Athletes, near goal weight
−500 kcal/day	1,777 kcal	~0.5 kg	Most people — recommended starting point
−750 kcal/day	1,527 kcal	~0.75 kg	Significant fat to lose; experienced dieters

For this example, the recommended fat loss target is 1,777 kcal/day (2,277 − 500). Use the Calorie Deficit Calculator to get your personalised daily target and see a projected timeline to your goal weight.

Based on: Hall KD, et al. "Quantification of the effect of energy imbalance on bodyweight." The Lancet. 2011;378(9793):826–837. PubMed ↗

When to Recalculate Your Deficit

Your calorie deficit target is not static — it must be updated as your weight changes. As you lose body mass, your BMR decreases, and so does your TDEE. A deficit of 500 kcal/day at your starting weight may shrink to 200 kcal/day after losing 8–10 kg — explaining why progress naturally slows even with perfect adherence.

Rule of thumb: recalculate TDEE and update your calorie target every 4–6 kg of weight lost. This prevents the situation where your effective deficit gradually disappears without any apparent cause.

The Protein Rule: Non-Negotiable During a Deficit

Once you have your daily calorie target, the most important single variable for determining what you lose (fat vs muscle) is protein intake. The evidence-based target for active individuals in a deficit is 1.8–2.4 g of protein per kg of body weight per day.

For the 72 kg woman in our example: 72 × 2.0 = 144 g/day of protein. At 4 kcal/g, that is 576 kcal from protein — leaving 1,201 kcal for carbohydrates and fat within the 1,777 kcal target. Protein should be set first; the remaining calories are distributed between carbs and fat.

See our full Weight Loss Guide for the complete framework including macros, exercise strategy, and long-term maintenance.

Frequently Asked Questions

How do I calculate my calorie deficit manually?

Three steps: Step 1 — calculate BMR using the Mifflin-St Jeor equation (Men: 10 × kg + 6.25 × cm − 5 × age + 5; Women: same minus 161). Step 2 — multiply BMR by your activity factor (1.2 for sedentary, 1.55 for moderately active) to get TDEE. Step 3 — subtract 500 kcal from TDEE to get your fat loss daily calorie target. Alternatively, use the TDEE Calculator and Calorie Deficit Calculator to automate steps 2 and 3.

How big should my calorie deficit be?

A 500 kcal/day deficit is the most widely recommended starting point, producing approximately 0.5 kg/week of fat loss while preserving muscle mass. A 250 kcal/day deficit is more appropriate for athletes or those close to their goal weight. Deficits larger than 750 kcal/day increase muscle loss, hunger, and hormonal disruption — and should only be used when someone has significant fat to lose and ideally under professional guidance.

What is the formula to calculate calorie deficit?

Daily calorie target = TDEE − deficit. Where: TDEE = BMR × activity multiplier. BMR (women) = (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161. BMR (men) = same + 5 instead of −161. Example: 1,469 kcal BMR × 1.55 activity = 2,277 kcal TDEE; 2,277 − 500 = 1,777 kcal/day fat loss target.

How often should I recalculate my calorie deficit?

Recalculate every 4–6 kg of weight lost. As your body weight decreases, your TDEE decreases, and the same calorie intake creates a progressively smaller deficit. Failing to update your target is one of the most common reasons fat loss slows and plateaus occur. At a minimum, recalculate at every 5% body weight reduction.

Should I use my goal weight or current weight for TDEE?

Use your current weight. TDEE equations estimate your current energy expenditure, not your future one. As you lose weight, your TDEE will decrease, and you should recalculate at each milestone. Using goal weight would underestimate your current needs and create an unnecessarily large initial deficit.

Is the Mifflin-St Jeor equation accurate?

It is the most accurate validated equation for predicting resting energy expenditure in healthy adults, outperforming the older Harris-Benedict equation in a 2005 comparison study (Frankenfield et al.). It is accurate to within 10% for approximately 82% of subjects. It tends to slightly overestimate BMR for very obese individuals and slightly underestimate for very lean, muscular individuals — for whom the Katch-McArdle equation (using lean body mass) is more accurate.

What activity factor should I use?

Use the multiplier that reflects your entire daily lifestyle — not just structured exercise. A person who exercises 4 days per week but sits at a desk for 8 hours otherwise is "lightly active" to "moderately active" — not "very active." Most people overestimate their activity level, which leads to overestimated TDEE and a smaller actual deficit than intended. When in doubt, choose the lower activity level and adjust upward if loss is faster than expected.

Can I calculate my calorie deficit without counting calories?

You can estimate your deficit without detailed food tracking by using the scale trend as feedback — if you are losing 0.4–0.6 kg/week on average, your deficit is approximately 300–500 kcal/day. If you are losing faster, the deficit is larger; if slower (or not at all), the effective deficit is smaller. This "feedback method" works but is less precise — tracking calorie intake periodically (even for 2–4 weeks) dramatically improves accuracy.

This article is part of our complete Weight Loss Guide.

Medical Disclaimer: Calorie prediction equations provide estimates, not exact measurements. Individual metabolic rates vary. Consult a registered dietitian or healthcare provider for personalised nutritional guidance, especially if you have any medical conditions.

Scientific References

Mifflin MD, St Jeor ST, et al. "A new predictive equation for resting energy expenditure in healthy individuals." Am J Clin Nutr. 1990;51(2):241–247. PubMed ↗
Hall KD, Sacks G, Chandramohan D, et al. "Quantification of the effect of energy imbalance on bodyweight." The Lancet. 2011;378(9793):826–837. PubMed ↗
Frankenfield D, Roth-Yousey L, Compher C. "Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults." J Am Diet Assoc. 2005;105(5):775–789. PubMed ↗