Figuring out how many calories you need each day can seem complicated. However, there are some simple steps you can take to get a rough estimate of your calorie needs. Here are some quick answers to common questions about calculating daily calorie needs:
How many calories does the average person need per day?
The average sedentary adult generally needs about 2,000 calories per day to maintain their weight. However, individual calorie needs can vary significantly based on factors like age, sex, height, weight, activity level, and health status.
Do men and women need different numbers of calories?
Yes, typically men need more calories than women. Estimated average calorie needs for adults by sex and age are:
| Age | Men | Women |
|---|---|---|
| 19-30 years | 2,400-2,600 calories | 1,800-2,000 calories |
| 31-50 years | 2,200-2,400 calories | 1,800 calories |
| 51+ years | 2,000-2,200 calories | 1,600-1,800 calories |
Men generally need more calories than women because men tend to have less body fat and more muscle mass, which burns more calories. Height and activity levels also play a role.
How do I factor in my activity level?
Your activity level is one of the biggest factors determining how many calories you need. More active individuals need more calories to fuel their lifestyles and workouts. Here are estimated calorie needs by activity level:
| Activity Level | Calorie Needs |
|---|---|
| Sedentary (little or no exercise) | 2,000-2,200 calories |
| Lightly active (light exercise 1-3 days/week) | 2,200-2,400 calories |
| Moderately active (moderate exercise 3-5 days/week) | 2,400-2,600 calories |
| Very active (hard exercise 6-7 days/week) | 2,800-3,000 calories |
To factor in your activity level, think about your typical exercise habits and lifestyle. Those who are more active need more calories to support their workouts and muscle mass.
Do I need fewer calories as I age?
Yes, calorie needs tend to decrease as we age. There are a few reasons for this:
- Metabolism slows down naturally with age
- Loss of muscle mass as we get older
- Typically less active compared to when younger
Older adults tend to move less, lose muscle, and burn fewer calories at rest. Calorie needs drop by about 10 calories per decade after age 25-30. Older adults should aim for lower calorie intakes to avoid weight gain.
How many calories should I eat to lose weight?
To lose weight, you need to eat fewer calories than your body uses each day. A deficit of 500-1000 calories per day from estimated needs is recommended for safe, sustainable weight loss. Here is an estimate of calorie deficits for weight loss:
| Daily Calorie Deficit | Expected Weekly Weight Loss |
|---|---|
| 500 calories | 1 pound |
| 750 calories | 1.5 pounds |
| 1000 calories | 2 pounds |
For example, if your calorie needs are 2,000 calories for weight maintenance, eating 1,500 calories per day would lead to an estimated 1 pound per week weight loss. Use a calorie calculator to determine your deficit.
What is the best formula for calculating calories?
There are a few different formulas used to estimate calorie needs:
Mifflin-St Jeor Equation
For adults, the Mifflin-St Jeor equation is considered one of the most accurate formulas for calculating basal metabolic rate (BMR), which is your minimum calorie needs. The formula is:
- For men: BMR = 10 x weight (kg) + 6.25 x height (cm) – 5 x age (years) + 5
- For women: BMR = 10 x weight (kg) + 6.25 x height (cm) – 5 x age (years) – 161
To factor in activity level, multiply the BMR by an activity factor between 1.2 and 1.9.
Katch-McArdle Formula
This formula uses your fat-free mass rather than total weight. The formula is:
- For men: BMR = 370 + 21.6 x (fat-free mass in kg)
- For women: BMR = 370 + 21.6 x (fat-free mass in kg)
This formula may provide a more accurate estimate for very muscular individuals.
Harris-Benedict Equation
This is an older but still sometimes used formula. The Harris-Benedict Equation is:
- For men: BMR = 88.362 + 13.397 x weight (kg) + 4.799 x height (cm) – 5.677 x age (years)
- For women: BMR = 447.593 + 9.247 x weight (kg) + 3.098 x height (cm) – 4.330 x age (years)
Similar to the Mifflin-St Jeor equation, you’d multiply the BMR by an activity factor to determine total calorie needs.
Should I use my BMR or TDEE to determine calorie intake?
Your BMR (basal metabolic rate) is the minimum number of calories your body needs to perform essential functions like breathing, blood circulation, and organ function. Your TDEE (total daily energy expenditure) is your BMR plus calories burned through daily movement and exercise.
To lose weight or maintain your weight, you should base your calorie intake on your TDEE rather than your BMR. Your TDEE accounts for the calories you burn through not just basic functioning but also daily living, which makes it a more accurate target calorie intake.
How do I calculate TDEE?
To calculate your TDEE:
- Calculate your BMR using the Mifflin St-Jeor equation or another formula.
- Multiply your BMR by an activity factor:
- Sedentary: BMR x 1.2
- Light activity: BMR x 1.375
- Moderate activity: BMR x 1.55
- Very active: BMR x 1.725
- Extremely active: BMR x 1.9
- The result is your estimated TDEE.
For example, if your BMR is 1,500 calories and you exercise moderately 3-4 days per week, your activity factor would be 1.55. Your TDEE would be 1,500 x 1.55 = 2,325 calories.
Should I use an online calorie calculator?
Online calorie calculators can provide a quick and easy way to get an estimate of your calorie needs. They use formulas like Mifflin-St Jeor and factor in information like your age, sex, height, weight and activity level.
Calorie calculator estimates provide a useful starting point. However, they may not be completely accurate as they cannot account for all individual factors that affect calorie needs. Use the calculator estimate as a baseline, then adjust up or down based on your own weight loss or maintenance results.
How accurate are activity trackers for calories burned?
Activity trackers like Fitbit® can estimate your calories burned through steps and workouts. However, these estimates may not be highly accurate. According to research, activity trackers tend to overestimate calories burned by 20-40% on average compared to more precise calculation methods.1
Activity trackers are better for tracking trends over time rather than absolute numbers. Look at your weekly or monthly average calories burned rather than daily numbers. Use the activity tracker estimates to inform your calorie intake, but do not view them as completely accurate measures.
Should I adjust my calorie intake frequently to account for weight changes?
You do not need to adjust your calorie intake frequently as your weight changes. Your calorie needs will remain relatively stable from week to week. Regularly increasing and decreasing calories can make it more difficult to maintain consistent healthy habits.
That said, you may need to adjust your intake if your weight loss stalls for 2-3 weeks or if you find you are constantly hungrier than expected at your current calorie intake. Adjust your calories by 100-200 per day at a time in response to your average weekly weight changes.
What is adaptive thermogenesis and how does it impact calories?
Adaptive thermogenesis refers to adjustments in your resting metabolic rate in response to changes in calorie intake and weight loss. It involves your body burning slightly fewer calories in an effort to conserve energy in the face of calorie restriction.2
The impacts of adaptive thermogenesis are relatively small, estimated to reduce daily calorie needs by 100-200 calories or so. This may slow but not completely halt weight loss. To counteract, you may need to adjust calories as needed based on your weight loss response.
Can genetics impact my calorie needs?
Genetics can play a role in determining calorie needs. Some people inherit a faster or slower metabolism that burns more or fewer calories at rest. Genetics account for 20-40% of your BMR.3 Environmental factors like diet and exercise also substantially impact your calorie needs.
Use your calorie calculator estimate as a starting point. If you find you are losing weight too rapidly or slowly at a certain calorie intake, adjust up or down accordingly based on your results. Your actual calorie needs may differ somewhat from calculated estimates due to genetic and other individual factors.
Should I eat back exercise calories?
Whether or not to “eat back” the calories you burn through exercise is a common question. Here are some general guidelines:
- Do not routinely eat back all exercise calories. Activity tracker estimates tend to be high.
- Eat back 30-50% of calories to account for extra hunger from workouts.
- On days with >90 minutes high intensity exercise, can eat back more calories.
- Monitor your weight and adjust intake up/down as needed to achieve goals.
Aim to fuel your workouts appropriately without overestimating extra calories needed. Adjust your intake based on hunger, energy levels, and your weight over time.
How often should I recalculate my calorie needs?
As a general rule, recalculate your calorie needs every 10 pounds of weight lost or yearly. Losing weight, gaining muscle, and aging can all impact your calorie needs over time.
Rather than strictly adhering to calculated numbers, use flexibility based on your results. If losing weight steadily at 2 pounds per week, no recalculation needed. Recalculate calories if weight loss stalls or if constantly hungrier than expected.
Conclusion
Estimating calorie needs can be complex but is mostly based on your age, sex, height, activity level, and goals. Use an online calculator or formula to get started, then adjust up or down based on your actual weight changes. Monitor your hunger cues, energy levels, and weekly weight to ensure you are fueling your body appropriately. Recalculate your numbers every 10 pounds lost or yearly as your needs may shift over time.
