How Many Calories Do You Actually Need?

The short version

• Your maintenance calories are an estimate. Formulas can be off by a few hundred calories either way.
• A deficit of 250 to 500 calories a day is a sensible starting point for most adults.
• Don't go below about 1,200 calories (women) or 1,500 (men) a day without medical supervision.
• Your scale trend over two to four weeks is the real test of whether your number is right.

Start with an estimate

Most calculators, including ours, use a formula called Mifflin-St Jeor. It estimates the calories you burn at rest from your height, weight, age and sex. That number is then multiplied by an activity factor to estimate your total daily burn, known as your maintenance calories or TDEE.

Most people overestimate their activity. If you're unsure between two levels, choose the lower one.

Turn it into a target

Subtract from your maintenance number:

• 250 calories a day: slower, easier to live with, and a good fit if you're close to your goal or very active.
• 500 calories a day: the classic starting point, often around a pound a week at first.
• Up to 750 calories a day: sometimes used for people with more to lose, and easier with a clinician's guidance.

Major obesity guidelines typically suggest about 1,200 to 1,500 calories a day for women and 1,500 to 1,800 for men as weight-loss targets, adjusted to the person. Eating below about 1,200 or 1,500 makes it hard to get enough nutrients and should be medically supervised.

Why the "3,500 calorie" rule misleads

You've likely heard that 3,500 calories equals a pound of fat, so cutting 500 a day loses a pound a week forever. It's a fair rule of thumb for the first few weeks and then it breaks down, because a smaller body burns less. Over a year it can overestimate weight loss substantially.

For a more realistic forecast, try the NIH's free Body Weight Planner, which accounts for this slowdown.

Test it against reality

A formula gives you a first guess. Your body gives you the answer.

1. Eat at your target for two to four weeks, as consistently as you can.
2. Weigh yourself several times a week and compare weekly averages, not single days. Here's why.
3. If the trend is falling at 0.5 to 2 pounds a week, keep going.
4. If nothing has moved after four weeks, first check how accurately you're tracking, then trim 100 to 200 calories or add more movement.
5. Recalculate after every 10 to 15 pounds lost, since your needs fall as you do.

You don't have to count

Counting is one tool, and it doesn't suit everyone. Many people reach a deficit using the plate method, eating more high-volume foods, or simply cutting out sugary drinks and most snacks. The estimate is still useful as background knowledge even if you never log a meal.

Sources

1. NIDDK: Body Weight Planner
2. CDC: Steps for Losing Weight
3. Jensen et al., Circulation (2014): AHA/ACC/TOS guideline for managing overweight and obesity

This guide is general information, not medical advice. Please check with a clinician before making big changes, especially if you have a health condition, take medication, or are pregnant. Read the full disclaimer.