What is a calorie deficit?
A calorie deficit means eating a little less than your body burns in a day. Your body makes up the difference with stored fat. That's how fat loss works, whether you count calories or not.
Every diet you've tried, from keto to points to fasting, works the same way underneath. They're just different ways of getting you to eat a little less.
How this calculator works
First it estimates how many calories your body burns at rest, using the Mifflin-St Jeor equation (the formula most dietitians use). Then it multiplies that by your activity level to get your maintenance calories, the amount that keeps your weight the same.
Your fat loss target is your maintenance minus 300 calories. Then it splits that into protein, carbs and fat, with protein high enough to keep you full.
How big should my calorie deficit be?
Smaller than you think. Most calculators tell you to cut 500 to 1,000 calories a day. That works for a few weeks. Then you're hungry, tired and cranky, and the weight comes back.
I lost 135 pounds and I've kept it off for over 15 years. The biggest lesson I learned: the right deficit is the one you can keep on a busy Tuesday, at a birthday party and on vacation. That's why this calculator uses a smaller one. It's a little slower at first, and you don't rebound.
Why am I not losing weight in a calorie deficit?
Small things add up. Cooking oil, sauces, bites while you cook and drinks can add a few hundred calories a day without you noticing.
Weekends erase the weekdays. 5 good days and 2 big days can land you right back at maintenance.
Water hides fat loss. Your weight can jump 2 to 5 pounds from one day to the next. Watch your weekly average, not one weigh-in.
Your numbers changed. As you lose weight, you burn a little less. Run the calculator again every 10 to 15 pounds.
Do I have to count calories forever?
No. Counting is a tool to learn what your portions look like. Most of my clients track for a while, then switch to eating the same simple meals by habit, and only check the numbers when the scale stalls.
Common questions
How many calories should I eat to lose weight?
Start about 300 calories below your maintenance calories. Your maintenance is what you burn in a day, based on your age, height, weight, sex and activity. The calculator above works out both numbers for you.
How fast will I lose weight with a 300 calorie deficit?
On average, about half a pound of fat a week, and often more in the first few weeks as water drops. It's slower than a crash diet, but it's a pace you can keep, which is what makes the weight stay off.
Is 1,200 calories a day a good idea?
For most adults, no. Most people burn well over 1,200 calories a day, so eating that little leaves you hungry and tired, and it usually ends in a rebound. Start with a smaller deficit you can live with.
How accurate is this calculator?
It uses the Mifflin-St Jeor equation, the formula most dietitians use. It's a strong starting estimate, not a perfect one. Follow it for 2 to 3 weeks, watch your weekly average weight, and adjust by 100 to 150 calories if you need to.
Do I have to exercise to be in a calorie deficit?
No. Your deficit comes mostly from food. But walking and a few strength workouts a week help you burn more, keep your muscle and feel better while you lose fat.
Weight loss coach. Lost 135 pounds and kept it off for over 15 years.