snapkin
The targets · Decision 4 of 14
How we calculate your calorie target
The calculator can estimate how many calories you need. It cannot promise how much muscle you will build. This page separates the sums the app does from the evidence behind them, and says what we decided because of it.
Last updated .
- What the app does
- Takes calories off for losing weight, adds them for gaining, and uses your estimated maintenance for “Maintain weight”. Protein also changes with the goal. Once a month it checks the target against what you logged and weighed.
- How sure we are Thin , One small study, or an engineering choice.
- The resting equation is well tested. Activity factors, exact pace limits and muscle-gain timelines are much less certain. Correct sums do not make a forecast for one person accurate.
Start with what you burn in a day, not what you burn at rest
Snapkin uses the simplified Mifflin–St Jeor equation: 10 × weight in kilograms + 6.25 × height in centimetres − 5 × age, then +5 for male or −161 for female. Mifflin et al. (1990) derived it from 498 adults aged 19–78. Our sums match that published equation. It predicts how much energy you burn at rest. Our API calls this “bmr”. If you do not state your sex, we use −78, the midpoint. That is our own convention, not another tested equation.
We multiply that estimate by your activity choice: 1.35, 1.50, 1.65, 1.80 or 2.00. These are calculator assumptions, not measurements of you. The result is your total daily energy expenditure (TDEE): what you burn in a day. Your goal adds to or takes from that total. So a deficit does not have to put your intake below what you burn at rest. Steps and watch calories are not added on top.
What the three options do
Loss defaults to 0.5% of your current weight per week, inside a range of 0.25–0.8%. Gain defaults to 0.2%, inside a range of 0.125–0.25%. If you pick a pace, it replaces the default, but it must stay inside those ranges. These defaults are what the server uses when it gets no pace. The loss setup screen picks its middle choice, “Normal”, when you do not answer. It lands close to 0.5%. Both directions use 7,700 kcal per kilogram, divided by seven days. So asking for 0.1 kg per week changes your intake by 110 kcal per day.
“Maintain weight” (stored as “both”) sets that change to zero. It does not work out fat loss and muscle gain separately. Loss and maintenance ask for 2.0 g of protein per kilogram of reference weight. Gain asks for 1.6 g. Reference weight is your current weight, but no higher than the weight that gives a BMI of 27.5. Protein is limited to 45% of your target calories, before rounding to 5 g. That BMI limit and that percentage are product rules of thumb, not a measurement of your lean mass.
The calories left over go to fat and carbohydrate. Fat gets whichever is larger: 0.6 g per kilogram of reference weight, or 45% of the calories left after protein. Carbohydrate gets the rest. This split is another default. It is not a recipe tuned for muscle growth.
Eating a little extra can support training. It does not buy a known amount of muscle
Helms et al. (2023) compared three groups over eight weeks of weight training: eating at maintenance, 5% extra, and 15% extra. 21 people took part and 17 finished. The people who gained weight faster gained more fat under the skin, measured with skinfold thickness, more clearly than they gained muscle thickness. But the 15% group improved their bench press more, and the authors could not rule out some extra biceps growth. This small, short trial is a reason to be careful with big surpluses. It does not tell us the one best surplus.
So our gain setting does more than change protein. It raises the calorie budget. But turning that extra into kilograms with the 7,700 rule, which is based on fat, cannot tell us kilograms of muscle. The sums know nothing about your training, or about how much of the gain is fat, lean tissue or water. The gain setup skips the pace question, uses a small default surplus, and shows no target date. Pace values saved earlier still work. No gain rate is shown as a muscle-growth forecast.
Can someone lose fat and gain muscle together?
Yes. Body recomposition is possible. It does not mean losing and gaining total body weight at the same time. In Garthe et al. (2011), 24 athletes trained with weights four times a week while dieting. The slower group increased lean body mass by 2.1% ± 0.4%. The faster group did not change in a way the statistics could detect, at −0.2% ± 0.7%. Lean mass is not the same as muscle. And this trial does not test Snapkin’s maintenance calories.
The evidence against matters too. Murphy and Koehler (2022) compared seven studies directly. Eating less held back lean-mass gains (effect size −0.57, p = 0.02). Their wider analysis linked a deficit of around 500 kcal/day with no lean-mass gain at all. That is a pooled link, not a fixed limit for everyone. Recomposition is something training can give you. A calorie setting cannot promise it.
Morton et al. (2018) pooled 49 weight-training studies with 1,863 people. They estimated that extra protein stops helping at around 1.62 g/kg/day. This supports our 1.6 g/kg starting point for gaining. It is not an exact need for every person. Our 2.0 g/kg choice for maintenance is a practical higher target. It is not evidence that maintenance calories cause recomposition. Eating protein does not replace lifting heavier weights over time.
Limits of the calculation
The deficit is limited to 35% of what we estimate you burn, before rounding. Then a calorie minimum applies: 1,500 for male, and 1,200 for female or unstated. The minimum is rounded up to a multiple of 50. Rounded protein stays below its limit. So rounding never pushes a target past either limit.
For a small, older, inactive person, the calorie minimum can leave no room for a deficit. It can also put a maintenance target above what we estimate they burn. The app must explain that conflict rather than promise the direction they picked. These minimums do not prove a diet is enough for a person. Neither does staying above what you burn at rest.
Hall et al. (2011) modelled how what you burn changes as your weight changes. The fixed 7,700 rule leaves those changes out. So it cannot give a reliable long-term timeline. That is one reason the app checks the target again after a month, with your own numbers.
The monthly check-in
Thirty days after your target starts, the app offers a check-in. It adds up what you logged and looks at the trend in your weight. Your body used the food you ate. If you lost weight, it used more than that. If you gained, it used less. So if you logged 2,150 kcal a day and lost 0.2 kg a week, your body used about 2,370 kcal a day. That number is measured on you. The formula's number is a guess for an average person.
A month is about the shortest time this works. Hall and Chow (2011) looked at daily weighing. They found it takes more than 28 days to see a change in what someone eats to within 300 kcal a day. So the check-in needs at least 20 days with meals and 4 weigh-ins. That is one a week. One weigh-in must be in the first week of the month and one in the last week. Those two matter most, because the trend is a line from the start of the month to the end. More weigh-ins in the middle help less. Weighing once a week gives a less exact trend than weighing every day. That is one more reason the target moves at most 250 kcal at a time. With less data, the check-in says what is missing and changes nothing. It asks again a month later.
It moves the target at most 250 kcal at a time. There is one exception. If your target is more than 35% below what you use, it goes straight up to that limit. It says you are on track when the measured number is within 150 kcal of your target. That is about the size of one person's error in this kind of sum. It leaves out days where you logged less than half your target. Those are usually days you stopped logging. And when you logged clearly more than your target, it never offers a lower one. Your weight matches what you ate. It offers a slower pace instead.
The first weeks of a diet can make the measured number a little too high. Water and stored carbohydrate go first. They hold less energy than fat. Heymsfield et al. (2012) measured about 4,860 kcal per kg of weight lost at week 4, and about 6,040 from week 6. Our sum uses 7,700. So the first check-in tends to suggest more food, not less. That is the safer side.
It comes earlier in two cases. One: your weight trend moves enough to change the formula's number by 50 kcal. That can happen at the earliest 14 days after the last check-in. Two: your trend reaches the target weight you set. Then it offers a target to keep your weight there. It uses the measured number when there is one.
The check-in assumes you logged everything you ate. If you often forget meals, it thinks your body uses less than it does. Then it suggests less food than you need. Weighing in is optional too. Without weigh-ins it shows what you logged. It changes nothing, unless a health store suggests a different activity level.
We checked the examples on this page against the calculator. The short-term protein and appetite findings do not take extra calories off the target. We do not subtract the 441 kcal/day from the feeding study from these targets. We do not add watch calories. The averages from the studies on game elements and logging are not used in the sums either.
Is the resting equation still the right one?
We checked this again in October 2026. There are newer equations that use only weight, height, age and sex. None of them does clearly better. The largest test we found is Bedogni et al. (2019), with 14,952 adults. Mifflin–St Jeor and the Henry equation did equally well. Both were within 10% of the measured value for 77–80% of people at a normal weight or overweight. For people with severe obesity, that was 60–64%.
Not every study agrees. Macena et al. (2022) reviewed 61 studies in people with overweight. They found the smallest average error with other equations. The equation may also read too high for some Asian groups. In Singapore Chinese adults it was 2.6–7.8% too high (Camps et al., 2016). Those studies are small. They do not agree with each other. So we do not add a correction for them.
Why the target does not allow for the camera’s error
Over a week of phone photos, Snapkin counted 90% of the calories in the weighed meals (how we measured that). Small misses cancel out over a week. This 10% undercount does not. So somebody who logs exactly their target really eats about 10% more. With a small deficit, that 10% can use up the whole deficit.
We still do not take the undercount off the target. There are three reasons.
- The undercount is not the same for every plate. Big plates come back low. Small ones come back high. Cutting everybody’s target would push some people too low.
- The target is less exact than the camera. The US energy equations from the National Academies (2023) have a standard error of 342 kcal a day for men and 241 for women.
- The US weight-loss guideline, Jensen et al. (2013), does not adjust targets for logging errors. It asks people to weigh themselves often. It also starts from a deficit of 500 kcal a day.
What we do instead. The setup screen now picks the Normal pace. That deficit is big enough that the undercount does not use it all up. The fix for the undercount itself belongs in the meal estimate, not in the target. And the monthly check-in measures what your body uses, from your own logs and weight. Both are counted the same way, so the undercount cancels out. Sanghvi et al. (2015) tested that kind of sum in 140 people over two years. For the group, it was within 40 kcal a day on average. For one person, it could be around 215 kcal a day out.
What the app says, and why
The choices read “Lose fat”, “Build muscle” and “Maintain weight”. Maintenance aims to keep your weight roughly stable, with protein to support training. Recomposition is a possible outcome, not a promise. The stored value stays “both” so existing accounts keep working.
Gain setups use the small default surplus and say that weight training is needed. Only fat loss asks for a pace and shows a rough target date. The server also hides gain and maintenance dates, even when an older version of the app asks for them. When the calorie minimum limits a plan, the plan says that the pace or direction you picked may not be possible.
The plan screen says the target is a starting point. It also names the day of the first check-in. Setup then asks how you will weigh in: from a health store, by hand with a Monday reminder, or not at all. The check-in itself shows one thing per screen: what you logged, your weight trend, your steps when a health store is connected, and what they add up to. Then it makes one suggestion. Nothing changes until you tap it. "Not now" asks again a week later. It only runs while you are losing or keeping weight. You can still edit your target by hand in Settings.