How does the weight loss calculator work out my goal date?

It finds your daily burn with the Mifflin-St Jeor equation and your activity, sets your calories 10 to 20% under it, and counts about 7,700 kcal per kilogram of body fat. Each week it lowers your burn a little as your weight falls, which is why the line curves and loss slows near the goal.

How many calories should I eat to lose weight?

Usually 10 to 20% under your daily burn, and not below 1,200 kcal a day for women or 1,500 for men without medical supervision. For many women in their 40s that lands around 1,500 to 1,700 kcal.

Why does my weight loss slow down?

A lighter body burns less, so the same calories make a smaller deficit. Losing muscle slows it further. Enough protein and some strength training help keep your daily burn up while you lose fat.

Is this weight loss calculator good for women over 40?

Yes. It sets protein first from your body, so the weight you lose is fat rather than muscle, which matters more after 40 when muscle naturally falls. It also adjusts the plan if you take a GLP-1 medication.

Yes, and it asks for no email. At the end you can get a free gift code for Protein Buddy to track a real day on iPhone or Android.

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Personalized and free

3 minutes

Weight loss calculator

Find out when you could reach your goal weight, how many calories a day get you there, and a plan of protein, carbs and fat that keeps your muscle while you lose fat.

Answer a few quick questions, tell us what you ate, and get your goal date with a plan built around your body.

The date you could reach your goal
Your daily calories and macros
Your real day compared with the plan

Find my goal date

FIND MY GOAL DATE

Protein Buddy

The short answer

How long will it take to reach your goal weight?

Eating about 20% under your daily burn, most women lose around half a percent of their body weight a week at first, then more slowly. A woman of 5 feet 5 inches going from 170 to 150 lb at a steady pace would get there in about 27 weeks on roughly 1,560 kcal a day. The calculator works out your own date week by week.

How the calculator works out your date

Find your daily burn. Resting energy from Mifflin-St Jeor (10 × kg + 6.25 × cm − 5 × age − 161 for women, + 5 for men), times your activity level.
Set a safe deficit. Eat 20% (steady) or 10% (gentle) under your burn, never below 1,200 kcal for women or 1,500 for men.
Turn the deficit into weight. About 7,700 kcal equals 1 kg of body fat, so a 500 kcal daily deficit is roughly 0.45 kg a week.
Recount every week. As your weight falls your burn falls too, so the weekly loss shrinks until you reach your goal.

Worked examples

Steady pace, computed with the method above. Your own date depends on your answers.
You	Daily calories	First weeks	To your goal
Woman, 45, 5′5″, 170 lb to 150 lb, walks 2 to 3 times a week	1,560	about 0.8 lb a week	about 27 weeks
Woman, 55, 5′4″, 200 lb to 170 lb, mostly sitting	1,430	about 0.7 lb a week	about 44 weeks
Woman, 40, 5′7″, 160 lb to 145 lb, trains 4 to 5 times a week	1,770	about 0.9 lb a week	about 18 weeks

Make the date real

What decides how fast you lose weight

The date is a projection. These are the things that move it.

The size of your deficit

Bigger is faster but harder to keep. 10 to 20% under your burn is the range most people can stay in.

Keeping your muscle

Muscle keeps your daily burn up. Enough protein and some strength work mean the weight you lose is fat.

What you really eat

Portions from memory run small. A tracked day shows the real calories and macros behind your progress.

Water and the scale

Day to day weight moves with water and food. Watch the trend over two to three weeks, not one morning.

More calculators

Your calories, macros and BMI

This calculator shares its method with the macro calculator, which splits your calories into protein, carbs and fat, and the BMI calculator, which shows your BMI and the healthy weight for your height.

A helpful estimate

Any equation is a starting point, and real weeks go up and down. Not medical advice: if you are pregnant, under 18, or managing kidney disease, diabetes medication or an eating disorder, ask a clinician what pace is right for you.

Check our sources

Research and guidance

Want to check our work? These sources explain the numbers we use.

Mifflin-St Jeor equationThe resting energy equation behind your daily burn.
Comparison of resting energy equationsRates Mifflin-St Jeor the most accurate for most adults.
Energy imbalance and body weightWhy weight loss slows as weight falls.
Muscle during weight loss reviewHow much of lost weight is muscle, with and without exercise.
Protein in weight lossWhy protein helps fullness and keeps muscle on fewer calories.
GLP-1 nutrition advisoryNutrition and pace during GLP-1 treatment.

Frequently asked questions

How long will it take to lose weight?: It depends on how far you are from your goal and how big your daily deficit is. Eating about 20% under your daily burn, most women lose around half a percent of their body weight a week at first, then more slowly as they get lighter. The calculator works it out week by week for your numbers.
How does the weight loss calculator work out my goal date?: It finds your daily burn with the Mifflin-St Jeor equation and your activity, sets your calories 10 to 20% under it, and counts about 7,700 kcal per kilogram of body fat. Each week it lowers your burn a little as your weight falls, which is why the line curves and loss slows near the goal.
How many calories should I eat to lose weight?: Usually 10 to 20% under your daily burn, and not below 1,200 kcal a day for women or 1,500 for men without medical supervision. For many women in their 40s that lands around 1,500 to 1,700 kcal.
Why does my weight loss slow down?: A lighter body burns less, so the same calories make a smaller deficit. Losing muscle slows it further. Enough protein and some strength training help keep your daily burn up while you lose fat.
Is this weight loss calculator good for women over 40?: Yes. It sets protein first from your body, so the weight you lose is fat rather than muscle, which matters more after 40 when muscle naturally falls. It also adjusts the plan if you take a GLP-1 medication.
Is it free?: Yes, and it asks for no email. At the end you can get a free gift code for Protein Buddy to track a real day on iPhone or Android.