A calorie deficit is a forecast, not a verdict.

The short version

How to start a calorie deficit

1. Estimate total daily energy expenditure, not just resting metabolism.
2. Choose a pace between roughly 0.25% and 1% of body weight per week.
3. Convert that pace into a daily deficit and check it against a practical intake floor.
4. Hold intake and weigh-in conditions reasonably consistent for at least two weeks.
5. Adjust by roughly 100 to 150 calories only when the trend gives you a reason.

Calculate my starting point

What a calorie deficit means

A calorie deficit exists when average energy intake is below average energy expenditure. Because both sides vary from day to day, a deficit is best understood across a week or longer rather than judged from one meal or one weigh-in.

The familiar 3,500-calorie-per-pound rule is a useful short-term conversion, not a complete model of human weight change. Water, glycogen, food mass, training, sleep, and metabolic adaptation all affect the scale. The NIDDK Body Weight Planner uses a dynamic model for longer forecasts for exactly this reason.

Step 1: estimate maintenance calories

Mifflin-St Jeor estimates resting energy expenditure from sex, age, height, and weight. Multiplying that estimate by an activity factor produces TDEE. If body-fat percentage is known, Katch-McArdle offers a lean-mass-based comparison.

No equation measures your metabolism. In a validation study of nonhospitalized adults, Mifflin estimates were still more than 10% away from measured resting metabolism in 22% of subjects. That is why Deficit Compass also shows multiple models and provides a calibration step.

Compare your TDEE across activity levels

Step 2: choose a pace your body size can support

The CDC describes about one to two pounds per week as gradual weight loss for many adults. A body-weight percentage is more portable: one pound is a very different demand for a 120-pound person than for a 300-pound person.

Gentle: 0.25% to 0.4% per week

Useful when training performance, hunger, or leanness makes a larger deficit costly. It requires patience but leaves more calories available.

Balanced: 0.4% to 0.75% per week

A practical default for many people. Deficit Compass starts at 0.6% and caps the resulting energy gap when needed.

Aggressive: 0.75% to 1% per week

May be tolerable for some people with more weight to lose, but it raises the cost to hunger, recovery, and adherence. Faster goals deserve professional guidance.

Step 3: test the forecast for two weeks

Track average daily calories and use a weekly average of scale weight, measured under similar conditions. Ignore the urge to react to individual days. After two consistent weeks, estimate trend-implied maintenance:

Observed maintenance ≈ average intake + (weekly pounds lost × 3,500 ÷ 7)

If you averaged 2,100 calories and lost 0.8 lb per week, the trend implies maintenance near 2,500 calories. This is still an estimate, but it is personalized evidence rather than a population equation.

Use the two-week calibration tool

When not to use an online calculator

Do not use this guide as a substitute for care if you are under 18, pregnant, breastfeeding, managing a medical condition or medication that affects weight, or have a current or past eating disorder. An intake estimate is not worth compromising health or recovery.

Unexpected fatigue, dizziness, menstrual disruption, declining training performance, persistent food preoccupation, or rapid weight change are reasons to stop treating the plan as a simple math problem and seek qualified help.

Sources

Primary references and public guidance

• Mifflin et al. (1990), predictive equation for resting energy expenditure
• Frankenfield et al. (2003), validation of resting metabolic rate equations
• CDC, gradual and steady weight loss guidance
• NIDDK Body Weight Planner

Written by Aaron Bergquist. The methodology has not yet been medically reviewed. Corrections are welcome at hello@deficitcompass.com.