How to find a calorie deficit that fits your weight loss goal

Weight loss is primarily about getting in fewer calories than you burn throughout your day or week. Common advice states that to lose a pound (about 0.5 kg), you have to cut 3,500 calories per week which translates to a daily caloric deficit of about 500-calories. That is how this memorable advice goes and it sounds right since it reflects the reality of losing body weight which calls for an energy imbalance over time.

Why the 3,500-calorie rule is less straightforward than it seems

First, everyone is different and so it doesn’t make sense that a 190 cm tall 130 kg man would lose weight at the same rate as a 160 cm tall 70 kg woman. These two bodies function differently, require different amounts of calories to maintain their current weight, and have a different body composition in terms of fat and lean tissue.

Second, your body changes as you lose weight so what worked in week one and two may not continue working into weeks 10 through 12, and vice-versa. As your weight changes, your daily energy expenditure also changes and so any rule which doesn’t account is obviously flawed. For a static number to hold across time, the energy gap would have to stay the same percentage-wise so that each pound lost represents the same change in stored energy.

The same deficit can produce different results

Expanding on the above example, if the adults eating 500 fewer calories than before start from comparable positions, then they will likely lose comparable amounts of body weight, even though it will likely not be a pound per week. A further factor is that their usual intake may not be equivalent to their maintenance caloric needs, so a reduction in intake might have different effects simply due to that.

A way to account for this is to adopt a dynamic energy-balance model which reflects the fact that a lighter body needs less energy at rest to go through daily life. It reflects changes in body composition as you lose weight, it includes metabolic adaptation and it shows how a calorie intake that initially produced a given weight loss may produce a smaller loss later on.

How to get your accurate calorie deficit

One way to do is to rely on GIGAcalculator’s calorie deficit calculator which uses the latest research on the topic to produce an estimate for your required calorie deficit much closer to what you would actually need.

It takes in personal measurements such as your weight, height, age, sex, and physical activity information, as well the target amount of weight to lose over a given timeframe. It also allows for current and future activity levels to differ, which reflects a typical situation where someone cuts back on calories, but also steps up their cardio or weightlifting efforts when trying to lose weight.

Losing five pounds is not a smaller version of losing fifty pounds

This is why the timeline matters. A modest weight loss and a much larger one would most likely follow different timelines since during a longer period of body weight change the body can become different enough for its original maintenance estimate to become unapplicable.

What type of body mass you lose matters as well since fat and lean tissue contain different amounts of stored energy. Similarly, body water can alter your weight without representing an equivalent change in tissue-stored energy. This is yet another reason to avoid using a blanked calories-per-pound lost as a forecasting tool.
The above is why multiplying a short-term caloric deficit estimate by five or ten does not result in a dependable long-term plan.

What a weight-loss calculator does differently

A calculator using the latest science takes your current situation and plots a map to your destination in terms of target weight, based on the time you set to reach it. It does so by using your total daily energy expenditure and what it needs to be at the specified weight goal. All of it is fed through the dynamic model which reflects how expenditure and body composition change as time goes on. All of this assumes you follow the plan, of course.

The most useful thing is that it doesn’t answer the question “How much should an average person cut from their diet?”, but rather: “What calorie deficit fits these specific circumstances?”. If you check your input carefully, provide a realistic description of physical activity, then the result would be a great starting point for your weight loss journey.

A good calorie deficit plan is one you can follow

Keep in mind that an estimate is only useful if you can abide by it day-by-day. How much hunger you can tolerate while fulfilling everyday responsibilities and without sacrificing adequate nutrition is something you still have to keep in mind. If anything, such a calculator can help you determine if the target you set for yourself is realistic or not.

For example, if you have previously found it difficult to reduce your intake by 300 calories a day, you know you would need to adjust your target weight or extend the timeframe if the estimated deficit is 600 calories per day.

The same applies if you have medical history, current medications, or other specifics which might make it difficult or impossible for your to achieve a given deficit. In such case, a caloric deficit calculator is your aid in setting an achievable goal.

A deficit is not the same as eating as little as possible

While it may be tempting to just start eating as little as you can manage each day, it is typically not a good strategy. The reason is that pushing yourself to the limit day after day is simply impossible for most people, and when they stop following their diet after a week or two, the consequences may be weight gain instead of weight loss.

Don’t be discouraged by daily swings of the scale

Since your body weight includes fat, water, glycogen, and what you have in your digestive tract, what you see on the scale each day may not reflect how much weight you are gaining or losing on that day.

Just eating more carbohydrates or salt can get you a pound or two of body water which would go as quickly as it came, once you reduce these foods. Similarly, a sharp drop in the beginning does not mean you are going to continue losing weight at the same pace going forward. More often than not, the opposite happens and the rate of weight loss becomes slower as time goes on.

It is worth knowing that the model behind GIGAcalculator’s calorie deficit tool explicitly accounts for fluid and glycogen changes as well as tissue changes.