About the Calorie Deficit Calculator

What it is

The Calorie Deficit Calculator is an educational energy-balance tool, not a weight-loss prescription calculator. It does two things: first it estimates your maintenance calories — the energy your body uses on a typical day at your current activity level — and then it explains what a calorie deficit means relative to that figure.

Maintenance calories are estimated using a two-step approach: your Basal Metabolic Rate (BMR) is calculated from your height, weight, age, and sex using either the Mifflin-St Jeor or Harris-Benedict formula, then multiplied by an activity factor to arrive at your total daily energy expenditure. Both formulas and metric or imperial inputs are supported. Everything runs in your browser — your details are never stored or sent to a server.

This tool deliberately does not output a prescribed calorie intake, set a target weight, or generate a cutting plan. Those decisions belong with a qualified professional who knows your full health picture.

Key features

What a calorie deficit is

A calorie deficit occurs when you consistently take in less energy than your body uses over time. Because the body draws on stored energy to make up the shortfall, a sustained deficit is associated with weight loss. A calorie surplus — consistently consuming more than you use — is associated with weight gain. Eating at roughly your maintenance level keeps weight stable.

The size of a deficit matters a great deal. Very large or very low calorie intakes can have serious health consequences, including muscle loss, nutritional deficiencies, hormonal disruption, and disordered eating patterns. Gradual, modest changes over time are widely regarded as safer and more sustainable than aggressive restriction.

How maintenance calories are estimated

What this tool does and doesn't do

It does: estimate your maintenance calories, show the BMR and multiplier breakdown, explain what a calorie deficit means conceptually, and present the three states of energy balance (deficit, maintenance, surplus).

It doesn't: prescribe how many calories to eat, generate a goal-weight target, suggest a specific deficit size, produce "lose X kg by [date]" projections, or include any aggressive or very-low-calorie presets.

This distinction is intentional. Personalised calorie targets involve health history, body composition, medications, and goals that no calculator can assess. A doctor or registered dietitian can account for all of those and give guidance that is actually tailored to you.

Important: this is not medical or dietary advice