A moderately active woman who stands 5’6″ typically needs between 1,800 and 2,200 calories per day to maintain her current weight. That range is wide because your exact number depends on your age, how much you move, and your body composition. A 25-year-old who exercises regularly will land near the top of that range, while a 55-year-old with a mostly sedentary routine will land closer to the bottom.
How Your Baseline Is Calculated
Your body burns a baseline number of calories just to keep you alive: breathing, circulating blood, maintaining body temperature, repairing cells. This is your resting metabolic rate, and it accounts for roughly 60 to 70 percent of the calories you burn each day. The most widely used formula for estimating it takes your weight in kilograms, your height in centimeters, and your age, then runs them through a simple equation. For women, the math looks like this: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161.
For a 5’6″ woman (167.6 cm), here’s what that produces at a few different ages and a weight of around 140 pounds (63.5 kg):
- Age 25: roughly 1,404 calories at rest
- Age 35: roughly 1,354 calories at rest
- Age 45: roughly 1,304 calories at rest
- Age 55: roughly 1,254 calories at rest
These numbers represent what your body burns doing absolutely nothing. To get your actual daily need, you multiply by an activity factor: 1.2 for sedentary (desk job, minimal exercise), 1.375 for lightly active (light exercise one to three days a week), 1.55 for moderately active (exercise three to five days a week), or 1.725 for very active (hard exercise six to seven days a week).
Calorie Estimates by Age and Activity Level
Plugging a 5’6″, 140-pound woman into those calculations produces the following daily maintenance estimates. These are the calories needed to stay at the same weight.
- Age 25, sedentary: ~1,685 calories
- Age 25, moderately active: ~2,176 calories
- Age 35, sedentary: ~1,625 calories
- Age 35, moderately active: ~2,099 calories
- Age 45, sedentary: ~1,565 calories
- Age 45, moderately active: ~2,021 calories
- Age 55, sedentary: ~1,505 calories
- Age 55, moderately active: ~1,944 calories
If you weigh more than 140 pounds, your numbers will be higher because a larger body requires more energy to maintain. If you weigh less, they’ll be lower. Every 10 pounds of body weight shifts your resting metabolism by roughly 50 to 70 calories per day.
Why Your Needs Drop With Age
You’ll notice the estimates above shrink by about 50 calories per decade. That’s not a coincidence. Resting energy expenditure decreases by approximately 4 calories per year, even after accounting for changes in body composition. Over 20 years, that adds up to roughly 80 fewer calories your body burns at rest each day.
Part of this decline comes from gradual muscle loss. Muscle tissue burns about 4.5 to 7 calories per pound per day at rest, which doesn’t sound like much until you consider that losing five or ten pounds of muscle over the decades meaningfully lowers your daily burn. This is one reason strength training becomes increasingly valuable as you age: maintaining muscle helps keep your metabolism from sliding as fast as it otherwise would.
How Body Composition Changes the Math
Two women who are both 5’6″ and 140 pounds can have noticeably different calorie needs depending on how much of that weight is muscle versus fat. Muscle tissue is metabolically active, burning roughly 5 to 7 calories per pound per day at rest. Fat tissue burns closer to 1 to 2 calories per pound per day. So a woman with more lean mass will have a higher resting metabolism than someone at the same height and weight who carries more body fat.
Your internal organs actually drive the biggest portion of your resting calorie burn. The brain, liver, heart, and kidneys have metabolic rates 15 to 40 times greater than an equivalent weight of muscle. You can’t change the size of your organs, but this helps explain why the formula above is only an estimate. Individual variation in organ size and efficiency means two people with identical stats on paper can differ by 100 to 200 calories per day in actual metabolic rate.
Calories for Weight Loss
If your goal is to lose weight, the general guideline is to reduce your daily intake by about 500 calories below your maintenance level. This typically produces a loss of about half a pound to one pound per week. For a moderately active 35-year-old woman at 5’6″, that would mean eating around 1,600 calories per day instead of 2,100.
Dropping below 1,200 calories per day is generally not recommended without medical supervision. Very low intakes make it difficult to get adequate nutrition, and your body tends to respond by slowing its metabolism further, which makes sustained weight loss harder over time. A moderate deficit that you can maintain for months will almost always outperform an aggressive one that lasts a few weeks.
Your actual rate of loss will vary depending on your starting weight, activity level, and how consistently you maintain the deficit. People with more weight to lose often see faster initial results, partly because their higher body weight means a larger calorie burn to begin with.
Calories During Pregnancy and Breastfeeding
Calorie needs shift significantly during pregnancy, but not right away. During the first trimester, your energy requirements are essentially the same as before pregnancy. The increase kicks in during the second trimester, when you need about 340 additional calories per day, and rises to roughly 450 extra calories per day in the third trimester.
Breastfeeding requires even more energy than late pregnancy. Women who are nursing need approximately 500 additional calories per day beyond their normal non-pregnant intake. For a moderately active 5’6″ woman, that could mean eating around 2,500 to 2,600 calories per day while breastfeeding. These numbers help explain why many women feel noticeably hungrier during nursing than they did while pregnant.
Finding Your Personal Number
The estimates above give you a solid starting range, but your real maintenance calories may be somewhat higher or lower. The most practical way to find your actual number is to track your food intake and weight for two to three weeks without deliberately changing your habits. If your weight stays stable, you’re eating at or near your maintenance level. If it trends up or down, adjust by 100 to 200 calories and observe again.
Activity trackers and fitness watches can help refine your estimate, but they tend to overestimate calorie burn from exercise by 15 to 30 percent. Use them as a rough guide rather than a precise measurement. The scale, combined with how your clothes fit and how your energy feels over a period of weeks, gives you more reliable feedback than any single calculation.