When you are working hard to lose weight, you will likely be weighing yourself at least once a week, if not more often. But, have you ever stepped on the scale every day for days in a row and found yourself asking, “Why does my weight fluctuate so much?“
Daily weight fluctuations are not only common but expected, as numerous factors can affect how much you weigh at any given point in a day.
Knowing how much your weight can fluctuate in a day, as well as the factors that cause daily weight fluctuations, can help you understand why your weight changes throughout the course of the day or from one day to the next.
This can hopefully help prevent momentary panic or a feeling of hopelessness when you seem to suddenly gain weight over the course of a day or between two different days.
In this article, we will cover some of the factors that affect daily weight fluctuations, and then we will try to answer the question: how much does your weight fluctuate in a day?
We will look at:
- Why Does My Weight Fluctuate So Much?
- Is It Normal for Your Body Weight to Fluctuate?
- Daily Weight Fluctuations: How Much Can Your Weight Fluctuate In A Day?
Let’s get started!
Why Does My Weight Fluctuate So Much?
If you weigh yourself every day or even multiple times per day, you will likely notice that your weight fluctuates daily at different points of the day and often from one day to the next.
This can make it difficult to know if you are actually losing weight, gaining weight, or just maintaining your weight and if your weight loss plan is working or not.
The good news is that daily weight fluctuations are normal.However, that does not make it any easier to understand if your weight is going in the desired direction if the scale is always showing a different number every time you weigh yourself and that weight is bouncing around rather than trending in the same direction.
Because there are numerous factors that affect your body weight when you step on a scale, health and fitness experts recommend using additional measurement tools besides just a regular scale to assess your weight loss progress.
Other supplementary body fat measurements are often less sensitive to daily fluctuations and can help provide a more complete picture of whether you are losing weight or gaining weight.
Examples include taking circumference measurements with a tape measure, taking weekly photographs either naked or in skin-tight clothing from both the front and side, getting your body fat percentage assessed periodically, and assessing the fit of your clothing.
However, although it is highly recommended that you also take circumference measurements and photographs to look at your changing body shape if you are trying to lose weight or gain muscle, the truth is that stepping on the scale is still the go-to method that most people use to see if they are losing weight.
Therefore, rather than ignore some of the inherent downsides of relying on a bathroom scale to inform you of your weight loss results or weight changes, it makes sense to just try to understand the limitations of weighing yourself by understanding factors that affect daily week fluctuations when you step on the scale.
Is It Normal for Your Body Weight to Fluctuate?
Ultimately, when you stand on a body weight scale, the scale is measuring your body mass multiplied by the acceleration due to gravity, which is what we call “body weight.“
The scale is not differentiating between any different types of tissue, such as fat, muscle, bone, blood, etc.
Even body weight scales, which use bioelectrical impedance to try to assess the relative percentage of body fat versus lean body mass, are inherently prone to error and are finicky and sensitive to things such as hydration status.
However, as much as a body fat scale can be somewhat inaccurate and prone to sensitivities in the readings, stepping on a regular scale is even more susceptible to various factors that will ultimately cause you to weigh more or less.
As mentioned, a regular scale is really looking at your entire body mass under the influence of gravity.
This means that factors such as how much undigested food is still in your stomach and digestive tract, how much urine is in your bladder, if and when you have last moved your bowels, if you are dehydrated after a sweaty workout or you’ve just guzzled a large bottle of water, among others, can impact how much you weigh when you step on a scale.
Furthermore, since you are eating and drinking, urinating and defecating, and potentially sweating or working out at numerous points in the day, daily weight fluctuations can be rather significant.
As an extreme scenario, imagine someone who wakes up and uses the bathroom, both urinating and moving their bowels and then steps on the scale before drinking or eating anything for the day.
This is often the lowest weight of the day because you have been fasting overnight from the overnight fast, you have voided urine and feces from your body, and you get somewhat dehydrated overnight as you sleep.
Then, imagine that person is a runner and goes for a relatively long or intense run in the sun and sweats a lot.
Even if you are hydrating while you run, most people find that their hydration during exercise, such as running, does not keep pace with their sweat rate, particularly during high-intensity workouts or long runs.
Thus, if this person weighs themselves before having a post-workout snack and rehydration beverages, their weight will be even lower.
Now, let’s imagine this person goes about their day and has a big post-run smoothie and hearty breakfast and continues to eat well and hydrate through the day.
If they weighed themselves after a big breakfast and mid-morning snack before peeing again, they might be several pounds heavier.
Their weight may continue to creep up over the course of the day as they eat more food and the digestive system has yet to create a sizable bowel movement and hydration status returns to normal, rather than in the post-workout, post-wake-up dehydrated state.
Daily Weight Fluctuations: How Much Can Your Weight Fluctuate In A Day?
Over the course of the day, your weight may fluctuate as much as 1–2 kilograms (kg) or 2.2–4.4 pounds for the average adult.
It might be even more significant if you are doing vigorous exercise and not hydrating well during the workout and weigh yourself right afterward.
If you step on the scale at different points in the day, you will catch your body at various stages of hydration, stomach/intestinal fullness, etc.
This will cause you to see your body weight going up and down on the scale across different times of the day.
It is also common to see daily weight fluctuations from one day to the next.
Even if you weigh yourself first thing in the morning every day, you may weigh more one day than the next based on exactly what you ate and drank the day before and where you are in your digestion and urination cycle.
Most people aren’t completely regimented in what they eat and drink, so one might have more food or fluid one day, which will cause you to weigh more the next day, or you might not hydrate well one day, causing you to weigh less the following day.
What you eat and drink also plays a role in your daily weight fluctuations.
Foods that are high in sodium cause water retention, so you will weigh more the morning after a salty dinner, such as if you eat out at a restaurant, enjoy fast food, have a salty canned soup or other processed food, or eat salty snacks like popcorn, chips, or pretzels.
On the opposite end of the spectrum, potassium encourages water excretion and helps balance out sodium levels.
Therefore, if you have eaten a lot of foods high in potassium, such as watermelon, avocados, celery, bananas, mushrooms, etc., daily weight fluctuations may go in the downward direction if your body is accustomed to these foods and you suddenly have a lot of potassium.
Like sodium, alcohol also causes water retention.
In fact, studies suggest that people weigh the most on Sunday night after a full weekend of eating out and drinking alcohol, and body weight tends to be lowest on Friday morning after a week of a more disciplined diet and less alcohol consumption.
Therefore, after a night at the bar drinking several beers or having a couple of cocktails and some bar food will likely cause you to suddenly gain weight from one day to the next.
However, again, this is not true fat gain, but rather your weight has temporarily increased due to water retention.
Caffeine is also a diuretic, so if you have a lot of coffee, green tea, black tea, energy drinks, or other caffeinated beverages one day, you might be somewhat dehydrated the next day due to excess fluid excretion, which can cause you to weigh less due to your lower body fluid status.
For biological females who have a menstrual cycle, there can also be rather significant daily weight fluctuations due to hormonal changes during the menstrual cycle.
In the first couple of days before your period and the first and second days of the menstrual cycle, your weight tends to be higher due to the hormonal milieu, which causes increased water retention.
This water weight should be released during your period and other stages of the menstrual cycle.
Lastly, if your weight fluctuates daily and from one day to the next, it could be the result of certain medications.
Diuretics will cause your weight to decrease because they encourage the excretion of water from the body.
Other medications, such as some tricyclic antidepressants, lithium, insulin, certain birth control medications, steroids, and certain antihistamines, can cause water retention and will cause changes in body weight in the upward direction.
Due to the sensitivity of a regular scale in assessing actual fat loss because of the complication of the factors that can cause daily weight fluctuations, it is often best to weigh yourself first thing in the morning after using the bathroom and before exercising.
Some studies suggest daily weighing is best, but this can lead to obsessiveness for some people.
Then, look at the trend in your body weight measurements: is your weight generally going down, staying the same, or going up?
Although daily changes in body weight of around 1–2 kilograms (kg) or 2.2–4.4 pounds over is normal, if you are experiencing more significant fluctuations in body weight, you should speak with your doctor about other underlying issues.
Furthermore, if you are trying to lose weight and have trouble tracking weight loss progress due to variations in your body weight from one day to the next, consider weighing yourself less frequently and adding supplementary assessments of weight loss.
You can learn more about measuring body composition here.