How many calories should I eat a day? A starting point

Search "how many calories should I eat" and you get a dozen different numbers. That's because there isn't one number for everyone. Your body, your age, your size and how much you move all change the answer. What you can get is a sensible estimate to start from, then adjust as you learn how your own days feel. Here's how that estimate is worked out.

Quick answer: how many calories should I eat a day?

There's no single right number. A common starting point is your maintenance calories: the estimated amount your body uses in a day. It's usually worked out with the Mifflin-St Jeor equation, then multiplied by an activity factor. The result is an estimate, not a prescription. This is general information, not medical advice.

What are maintenance calories?

Maintenance calories are the amount of energy your body is estimated to use in a typical day. That energy goes to three things:

• Basal metabolic rate (BMR). What your body spends just keeping you going at rest: breathing, circulation, temperature.
• Movement. Walking, chores, workouts, fidgeting.
• Digesting food. A smaller share, but it's part of the total.

Add those up and you get a total daily energy estimate. Many people use that figure as a reference point when they think about how much to eat. It's a reference, not a rule.

The Mifflin-St Jeor estimate

The Mifflin-St Jeor equation is a commonly used way to estimate BMR from weight, height and age. It looks like this:

• Men: 10 x weight (kg) + 6.25 x height (cm) - 5 x age + 5
• Women: 10 x weight (kg) + 6.25 x height (cm) - 5 x age - 161

It's popular because it's simple and only needs three measurements. It's still a population-level estimate. Two people with the same numbers can differ by a few hundred calories a day in real life.

Activity levels: the multiplier step

BMR only covers rest. To estimate a full day, the result is commonly multiplied by an activity factor:

• Sedentary (desk job, little exercise): about 1.2
• Lightly active (light exercise 1 to 3 days a week): about 1.375
• Moderately active (exercise 3 to 5 days a week): about 1.55
• Very active (hard exercise most days): about 1.725
• Extremely active (physical job plus training): about 1.9

Most people overestimate how active they are. If you're between two levels, picking the lower one is a common choice, and you can revisit it later.

A worked example (illustrative)

These numbers are for illustration only, not a recommendation for anyone.

Take a 35-year-old woman, 70 kg, 165 cm:

1. BMR: 10 x 70 + 6.25 x 165 - 5 x 35 - 161 = 700 + 1,031 - 175 - 161 = about 1,395 calories
2. Lightly active (x 1.375): about 1,918 calories

So her estimated maintenance is roughly 1,900 calories a day. Had she picked sedentary (x 1.2), it would be about 1,674. Moderately active (x 1.55) gives about 2,162. The activity guess moves the answer by hundreds of calories, which is why the final figure is a range you test, not a fact you obey.

If you'd rather not do the arithmetic, the calorie calculator does it for you.

Why this is only a starting point

Every part of the calculation is an average. Formulas can't see your muscle mass, your sleep, your medications or how much you really move. Day-to-day intake also varies, so one day tells you very little.

A few honest limits:

• The equation estimates. It's built from group data, not measurements of you.
• Activity is a guess. Step counts and workouts help, but they're rough too.
• Your needs change. Age, season, training and life events all shift the number.
• Food numbers are estimates as well. Calories in a meal are never measured to the last unit, so you're comparing one estimate with another.

That last point matters. Treat your target as a band, not a bullseye. If your target is 1,900, a day at 1,800 or 2,000 is not a failure or a win.

Should you eat more or less than maintenance?

That depends on your goals and your health, and it's a conversation for your doctor or dietitian, especially if you have a medical condition, are pregnant or breastfeeding, are under 18, or have a history of disordered eating. We won't tell you what to aim for, and no calculator should either. Not medical advice: talk to your care team about what's right for you.

How to use your number in real life

A number on a screen only helps if it connects to what you eat. A simple way to use it:

1. Work out your estimate with the equation or a calculator.
2. Write down what you eat for a week or two, without changing anything. See calorie counting for beginners for an easy way to start.
3. Look at your typical day compared with your estimate.
4. Adjust slowly, with your care team if it's a health matter, and check in again after a couple of weeks.

If you track, keep it calm. Our post on tracking calories without obsessing covers how to look at numbers without letting them run your day.

Where a food journal fits

An estimate of what you need is only half the picture. The other half is what you actually eat, and that's where most people lose interest, because logging can feel slow.

Ramen is built to make that half quick. You type what you ate in plain words, one line per food, and calories and macros appear beside each line, usually in about 2 seconds. Ramen works out calorie and macro targets from your goal, body and activity, and it reads weight, height and activity from Apple Health. Every number is an estimate, and when it's less sure you'll see a "~". Tap a number and it explains in plain language how it was worked out. If you're comparing apps, our calorie tracker app page shows how it works. For more on the Health connection, read Apple Health and calorie tracking.

The short version

• There's no one number that suits everyone.
• Maintenance calories are an estimate of what you use in a day.
• Mifflin-St Jeor plus an activity factor is a commonly used way to get a starting figure.
• Pick the lower activity level if you're unsure.
• Treat the result as a range to test, not a rule.
• For health questions, ask your care team.

Try it with a food journal

If you want to see how your days compare with your estimate, writing down what you eat is the easiest way. Ramen is coming soon to iPhone. Join the waitlist and we'll send you one email when it's out.