Find your maintenance calories
Your maintenance calories are how much you'd need to eat each day to keep your weight where it is. Every deficit is measured from that line, so it's worth getting close. A calculator gets you started, and two weeks of your own numbers will tell you the rest.
Start with an estimate
Maintenance is the same number as your total daily energy expenditure (TDEE): everything your body burns in a day. Calculators estimate it in two steps:
- Your energy use at rest (BMR), worked out from your age, sex, height and weight. The Mifflin-St Jeor equation is the usual choice, as it's the most accurate of the common formulas.
- An activity multiplier, from around 1.2 if you mostly sit to 1.9 if you do hard physical work or train most days.
The TDEE calculator does both for you. Treat the result as a starting point. Even the best formula is more than 10% out for a fair share of people, and 10% of 2,200 kcal is 220, almost half a typical deficit. The activity level is the bigger guess: most people pick one level higher than their week really is. If you're unsure between two, choose the lower.
How far to trust your watch
Fitness trackers estimate calories burned from your heart rate and movement. They're good at counting steps and measuring heart rate, and much less good at turning that into calories. When Stanford researchers tested seven popular wrist devices, none measured energy use accurately: the best was out by 27% on average and the worst by 93%. Gym machines tend to be generous too.
That doesn't make a tracker useless. Its errors are fairly consistent, so if it reads 15% high it'll usually read 15% high every day. As long as you check it against your weight, as below, a consistent error gets corrected along with everything else.
Find your real number from your own log
Your weight and what you eat already tell you what you burn. If you ate a known amount and lost weight, your body made up the difference from its stores. To use that:
- Log everything you eat and drink for at least two weeks. Three or four is better.
- Weigh yourself every morning, after the loo and before eating or drinking.
- Average your weight for the first week and for the last.
- Work out: maintenance = average daily calories in + (kg lost per week × 7,700 ÷ 7). If you gained weight, take it away instead.
A worked example
Say you ate 1,800 kcal a day on average for two weeks, and your weekly average weight went from 80.2 kg to 79.7 kg. That 0.5 kg is about 3,850 kcal, or 550 kcal a day. Your body burned 550 kcal a day more than you ate, so your maintenance is about 1,800 + 550 = 2,350 kcal.
The neat part is that this number already allows for how you count. If you tend to underestimate portions a little, your maintenance comes out a little lower too, and your deficit stays honest as long as you keep counting the same way.
Getting a fair reading
- Skip the first week of a new diet. Cutting back usually drops a kilogram or more of water early on, which would make your maintenance look far higher than it is.
- Allow for your cycle. If you have periods, water retention can hide a week's progress. Four weeks, or comparing the same point in each cycle, gives a truer answer.
- Log the awkward days. A rough figure for a meal out is far better than a blank, which would make your average look lower than it was.
Keep it up to date
A lighter body takes less energy to run and to move about, so your maintenance falls as you lose weight, by very roughly 20 kcal a day for every kilogram. It's small at first, but after 10 kg it's around 200 kcal, enough to stall progress if your target hasn't moved. Recheck your number every month or so, or after every 5 kg.
Using it in the tracker
On the week page, set your usual calories out to your maintenance figure. It then fills in on any day you only enter calories in, marked as an estimate until you change it. If you'd rather use your watch's figure on a given day, type it over the estimate. Next, you need to decide how far below maintenance to eat.
Questions
Are maintenance calories the same as TDEE?
Yes. Total daily energy expenditure (TDEE) is what you burn in a day, and eating that much keeps your weight steady, so both terms mean the same number.
How long does it take to find my maintenance calories?
Two weeks of logging and daily weighing gives a first answer. Three or four weeks gives a more reliable one, as daily water swings even out.
Should I eat back the calories my watch says I burned?
Only if your maintenance figure leaves exercise out. If you use your watch total as calories out each day, the exercise is already counted. Watch figures often run high, so check them against your weight trend.
Does my maintenance change as I lose weight?
Yes. A lighter body uses less energy, so recheck your number every month or so, or after every 5 kg lost.
Sources
- Mifflin MD, St Jeor ST, Hill LA, et al. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 1990; 51(2): 241–247.
- Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association, 2005; 105(5): 775–789.
- Shcherbina A, Mattsson CM, Waggott D, et al. Accuracy in wrist-worn, sensor-based measurements of heart rate and energy expenditure in a diverse cohort. Journal of Personalized Medicine, 2017; 7(2): 3.
- Hall KD, Sacks G, Chandramohan D, et al. Quantification of the effect of energy imbalance on bodyweight. The Lancet, 2011; 378(9793): 826–837.
This guide is general information, not medical advice. If you have a health condition, are pregnant, or have a history of disordered eating, talk to your GP or a registered dietitian before changing how you eat.