Free nutrition tool
Calorie & Macro Calculator
Get a transparent calorie starting point for maintain, lose or gain goals, plus protein, carb and fat ranges. The math uses Mifflin-St Jeor and an activity multiplier—not medical personalization.
Method & guardrails
Mifflin-St Jeor, made readable
The calculator separates the equation from the goal choice. That makes it easier to see what is estimated and what still needs a human decision.
1 · Estimate resting needs
Mifflin-St Jeor uses age, height, weight and the sex parameter selected for the equation to estimate resting energy expenditure. “Not specified” uses the midpoint of the equation constants.
2 · Apply activity
The resting estimate is multiplied by a standard activity factor: 1.20, 1.375, 1.55 or 1.725. This is an estimate of a typical day, not a lab measurement.
3 · Keep the goal conservative
Maintain uses about ±5%, lose uses about 5–15% below maintenance, and gain uses about 5–10% above it. The result never displays less than 1,200 kcal/day.
What the calculator cannot personalize
It does not know your medical history, body composition, appetite, lab values, pregnancy status or relationship with food. It cannot prescribe calories, macros, medication changes or doses. Treat the result as a conversation starter and follow qualified advice when your situation is complex.
Method & guardrails
What to keep in mind
These notes explain the estimate without turning it into a prescription.
Method & guardrails
1 · Estimate resting needs
Mifflin-St Jeor uses age, height, weight and the sex parameter selected for the equation to estimate resting energy expenditure. “Not specified” uses the midpoint of the equation constants.
Method & guardrails
2 · Apply activity
The resting estimate is multiplied by a standard activity factor: 1.20, 1.375, 1.55 or 1.725. This is an estimate of a typical day, not a lab measurement.
Method & guardrails
3 · Keep the goal conservative
Maintain uses about ±5%, lose uses about 5–15% below maintenance, and gain uses about 5–10% above it. The result never displays less than 1,200 kcal/day.
Method & guardrails
Estimates and lived results differ
An equation estimates a starting point; appetite, movement, medication, sleep and body composition can make real needs different.
Method & guardrails
Macro percentages are planning ranges
The macro split helps organize a plan. It is not a requirement to hit every gram or a prescription for a medical condition.
Method & guardrails
Check the trend, not one day
Compare the estimate with a multi-week trend and how you feel, then adjust with a qualified professional when needed.
Useful next steps
Practical examples
Small, visible steps help turn an estimate into a routine.
Example
A conservative calorie example
If maintenance is estimated at 2,000 kcal, a 5–15% loss range is about 1,700–1,900 kcal; it is not an instruction.
Protein
A protein-range example
At 2,000 kcal, a 25–35% protein planning split is about 500–700 kcal, or roughly 125–175 g.
Carbs
A macro-planning example
A 35–45% carbohydrate planning split at 2,000 kcal is about 700–900 kcal, not a required target.
Context
An equation is a starting point
Two adults with the same inputs can observe different real-world results because the equation cannot see every variable.
Trend
A trend check
Look at a few weeks of weight, appetite, activity and adherence rather than reacting to a single weigh-in.
Review
A practical review
Review the starting estimate after real observations and discuss major changes with a dietitian or clinician.
Use these cards as prompts for a calm conversation with your healthcare professional.
Common questions
Calories and macros, without false precision
What equation does this calculator use?
It uses the Mifflin-St Jeor equation for a resting estimate, then applies a standard activity multiplier. Goal ranges are conservative adjustments around estimated maintenance. The result is a starting point, not a measurement of your exact metabolism.
Why does the calculator ask for sex?
Sex is included because it is a parameter in the Mifflin-St Jeor equation. It is used only for that calculation and is not a statement about identity. Choosing “Not specified” uses a midpoint constant rather than forcing a choice.
Are the calorie and macro numbers medical advice?
No. They are educational estimates for planning conversations. Conditions such as pregnancy, diabetes, kidney disease, an eating-disorder history or intensive training can change what is appropriate; a clinician or dietitian can help you decide.
Why is there a lower calorie guardrail?
The calculator does not display a goal range below 1,200 kcal/day. That guardrail prevents an obviously low output from looking like an instruction, but it is not a universal safe minimum and does not make the result individualized.
What practical context should I keep with this result?
Calories are only one part of eating well on GLP-1. Pair this starting point with a protein-specific estimate and the foods you actually log.
How should I use the limits on this page?
It does not know your medical history, body composition, appetite, lab values, pregnancy status or relationship with food. It cannot prescribe calories, macros, medication changes or doses. Treat the result as a conversation starter and follow qualified advice when your situation is complex.
Sources
How this page is grounded
- Mifflin MD et al., “A new predictive equation for resting energy expenditure in healthy individuals,” The American Journal of Clinical Nutrition, 1990.
- NIDDK, Body Weight Planner.
- NIDDK, Your Game Plan to Prevent Type 2 Diabetes — starting calorie ranges and 1,200 kcal floor context.
- NIDDK, About the Body Weight Planner — adult and pregnancy/breastfeeding limitations.
Last updated August 7, 2026. This educational page follows our Medical Review Policy. Tell us about a correction.
Good estimates become useful when they meet real life.
Glowise helps you connect calories and macros with meals, hydration, weight and your GLP-1 routine.
