Why do I lose less weight than the math predicts?

Two reasons. First, the 3,500 kcal per pound rule assumes only fat loss; in reality you also lose muscle and water, especially early on. Second, your TDEE decreases as you lose weight because there is less body to maintain, and adaptive thermogenesis reduces metabolic rate beyond what mass loss alone explains. Recalculate your TDEE every 10 pounds.

Is a 1,000 kcal deficit safe?

Only with medical supervision. A 1,000 kcal per day deficit is at the edge of what is considered safe for adults with significant excess body fat, and only short term. Outside supervised settings, the risks include muscle loss, gallstones, hair shedding, and aggressive metabolic adaptation that makes regain easier.

Should I cycle calories on rest days vs training days?

Optional. Calorie cycling (lower on rest days, higher on training days) tracks weekly average more than daily numbers and can improve compliance for some people. The total weekly deficit is what drives weight change. There is no metabolic benefit to cycling beyond the psychology of bigger eating windows around hard workouts.

What if I am not losing weight at my deficit?

Most likely causes: TDEE overestimate (drop activity tier by one), tracking inaccuracy (food labels run plus or minus 20%; restaurant meals can be 50% over their reported calories), or adaptive thermogenesis at the 3 to 6 month mark. Reset by recalculating TDEE, tightening food logging for 7 days, and walking 30 minutes daily to lift NEAT.

The daily number that actually moves the scale

Jillian Foglesong Stabile, MD

FAAFP, DABOM · Reviewed June 10, 2026 · Energy balance

Sex assigned at birth (the equation uses this)

Age

Height (feet)

Height (inches)

Weight

Activity level

Goal

Pace

Screening estimate only, not a medical or nutrition prescription. Calorie needs vary with body composition, health conditions, and medications, and a licensed physician determines eligibility for any treatment. Individual results vary.

Chapter 01 · The math

How energy balance works

A sustained deficit causes weight loss; a surplus causes gain. The 3,500 kcal per pound rule is a first approximation, useful for setting a starting target.³ A more complete dynamic model adds adaptive thermogenesis: your TDEE drops over time beyond what mass loss alone explains, which is why predicted and actual loss diverge after the first month.²

Daily deficit	Approximate weekly loss	Who it suits
250 kcal	about 0.5 lb	Lean, slow and steady
500 kcal	about 1 lb	Most adults
750 kcal	about 1.5 lb	More to lose
1,000 kcal	about 2 lb	Physician supervision only

Deficits above 1,000 kcal per day belong under medical oversight.

Chapter 02 · The limits

What a safe deficit looks like

500 kcal per day produces about a pound per week for most adults. 750 kcal per day works for people with more to lose. Over 1,000 kcal per day requires physician oversight, because aggressive deficits carry real risks: muscle loss, gallstones, hair shedding, and faster metabolic adaptation. The calculator floors your target at 1,200 kcal for that reason.

The point: bigger deficits do not mean better results. Sustainable beats aggressive almost every time. Individual results vary.

Chapter 03 · The other direction

Gaining muscle instead

To gain muscle, run a 250 to 500 kcal per day surplus above TDEE paired with resistance training. Bigger surpluses add fat rather than muscle, since roughly a pound per week is the upper conversion rate. The calculator caps a gain surplus at 500 kcal for the same reason. If you are using a GLP-1 medication or have a medical condition, a licensed physician, not this calculator, sets the right target. Individual results vary.

Every medication on sipra is prescribed by a licensed physician, so your care always starts with a visit. Your sipra membership gives you ongoing access to those physician visits, so you can check in, adjust your plan, and ask questions whenever you need, without paying per visit. It is how we keep high-quality care convenient: one membership, physician access whenever you need it, and support at every step.

Sources

Mifflin MD et al. "A new predictive equation for resting energy expenditure in healthy individuals." American Journal of Clinical Nutrition. 1990;51(2):241-7. doi.org
Hall KD et al. "Quantification of the effect of energy imbalance on bodyweight." Lancet. 2011;378(9793):826-37. doi.org
Wishnofsky M. "Caloric equivalents of gained or lost weight." American Journal of Clinical Nutrition. 1958;6(5):542-6. doi.org

Compounded medications are not FDA-approved and require a patient-specific prescription. Brand names are trademarks of their owners; sipra is not affiliated with them.

General education, not medical advice. Last reviewed June 10, 2026 by Jillian Foglesong Stabile, MD, FAAFP, DABOM. Prices snapshot Energy balance. Individual results vary.