health · 2026-05-01

TDEE calculator (Mifflin-St Jeor)

Total daily energy expenditure using Mifflin-St Jeor BMR formula × activity factor, plus calorie targets for cutting / maintaining / building.

TDEE (calories/day)
2,689
Mifflin-St Jeor × activity factor

Inputs

Age (years)35
SexMale
Height (inches)70
Weight (lb)175
Activity levelModerate (3-5 sessions/wk)

Supporting metrics

BMR (calories/day at rest)1,735
Cut target (-20%)2,151
Maintain target2,689
Build target (+10%)2,958

About this calculator

TDEE — your real daily calorie burn

Total Daily Energy Expenditure (TDEE) = BMR × activity factor. It's the number that decides whether you lose, hold, or gain weight on a given diet.

The formula stack

  1. BMR (basal metabolic rate) — calories to keep you alive at rest. We use Mifflin-St Jeor, the most accurate of the common BMR estimators per direct calorimetry studies.
  2. Activity factor — multiplier for everything above resting (1.2 sedentary → 1.9 extreme).
  3. Goal adjustment — cut at TDEE × 0.8 (20% deficit), build at TDEE × 1.1 (10% surplus).

Why 20% cut and 10% build (not symmetric)

A 20% deficit produces ~1-2 lb/wk fat loss for most people — sustainable, preserves muscle if protein is high. Larger deficits compromise muscle and adherence.

For building, a 10% surplus is genuinely enough. You can't build muscle faster than ~0.5 lb/wk (advanced) to 1.5 lb/wk (newbie). A bigger surplus just adds fat, not muscle. The "dirty bulk" tradition is mostly an excuse to eat ice cream.

Real-world calibration

This calc is an estimate within ±10-15%. Track for two weeks at the calculated maintain number. If your weight is stable, the number is right. If it's drifting, adjust ±100-200 calories and retry. The math gives you the starting point — the scale gives you the truth.

FAQ

Mifflin-St Jeor vs Harris-Benedict vs Katch-McArdle?

Mifflin-St Jeor is the most accurate when body fat is unknown. Katch-McArdle is more accurate IF you have a reliable body fat % (DEXA, BodPod), because it's based on lean mass. Harris-Benedict was revised in 1984 but is still the least accurate of the three. Default to Mifflin-St Jeor.

I'm not losing on a 20% deficit — what gives?

Three usual culprits: (1) NEAT down-regulates — when you eat less, you unconsciously fidget less, walk slower, take fewer steps. (2) Tracking is off by 10-25% for most people who 'estimate' calories. (3) Water retention masks fat loss for 2-3 weeks. Track for 4 weeks before adjusting.

How often should I recalculate TDEE?

Every 5-10 lb of weight change, OR every 6-8 weeks during active cut/bulk. As you lose fat, BMR drops modestly (less mass to maintain). As you build muscle, BMR ticks up slightly. The activity multiplier matters more than the BMR drift.

Is the activity factor really that big?

Yes. The gap between 'sedentary' (1.2) and 'very active' (1.725) is ~500 calories/day for a 175 lb person. That's why two people the same size can need wildly different intakes. Be honest about your real activity, not the level you wish you were at.