Weight Fluctuation: How Much is Normal?

Charting your weight with a moving average helps smooth out the ups and downs to reveal the real story.

Monica Reinagel, MS, LD/N, CNS
5-minute read
Episode #199


By Monica Reinagel, M.S., L.D./N. and Jason Marshall, PhD

Jo writes:

“I’m not trying to lose weight, just to maintain. But I've noticed that my weight can vary by as much as 5 pounds throughout the week. I know that some amount of variation is normal but how do I know what my “real” weight is?”>

You’re absolutely right, Jo. Weight can fluctuate by several pounds from day to day (or over the course of a single day) without reflecting any actual loss or gain of fat or muscle tissue. Your weight can be temporarily affected by things like the amount of fluids you've consumed, the timing of your last workout, or…how to put this?...the status of your digestive processes. 

Indeed, some people find that weighing themselves is counter-productive. When I polled my Twitter and Facebook followers on how often they hop on the scale, several responded that they’ve thrown out their scales entirely.

Oprah Winfrey, for example, says she never steps on the scale because it ends up sabotaging her waist-control efforts. If her weight is up, she gets discouraged and loses motivation to stick to her eating plan. If her weight is down, she winds up eating too much because she figures she can afford to cheat. Instead, Oprah prefers to use the way her clothes fit as an indicator of how she's doing. 

The number on the scale obviously doesn’t tell the whole story. I often hear from people who start exercising and find that they drop inches or dress sizes but not weight. How you look and feel is definitely important. But I’m all too capable of ignoring or rationalizing things I don’t want to see. I could easily convince myself that those jeans that seem to be fitting more snugly must have spent too long in the dryer. Or that I just don’t like those particular jeans anymore. For me, anyway, stepping on the scale regularly is a useful reality check.

How Often Should You Get on the Scale?

Some weight loss experts recommend weighing in only once a week. I guess the idea is to keep you from worrying too much about the inevitable daily fluctuations and help you focus on your long term progress. But what if your weekly weigh-in day happens to coincide with a day when you’re at the high end of your normal variation? One solution is to weigh yourself every day but to chart your weight using a moving average. What’s a moving average, you ask? Thankfully, Jason Marshall, The Math Dude, is here to explain.

*** A Math Dude Exclusive! ***

Thanks Monica – I’m glad to help!

To understand what moving averages are and how to calculate them, we first need to make sure we understand good old-fashioned non-moving averages.

The word “average” can actually mean many things, but its most common meaning—the one we’re all familiar with—is what’s known as the mean. To find the mean of a group of numbers, just add them up and then divide by the size of the group. Let’s say you spend $5 for lunch on Monday, $8 on Tuesday, $4 on Wednesday, $6 on Thursday, and $12 for a really fancy lunch on Friday. To find out your average lunch expenditure for the week, you’d add up each of those numbers and divide by 5 to get $7. 

A moving average, on the other hand, is an average that slides through time. It’s a great way to see trends or changes in whatever you’re tracking…especially when things are changing relatively slowly or there’s a lot of variation in the numbers from day to day.

For example, let’s take Sandy. She’s trying to fit into a dress for her daughter’s wedding. To do that, she’s started a diet and exercise program and is keeping track of her weight. She records a starting weight of 150 pounds on Monday, then down to 148 pounds on Tuesday, back up to 151 pounds on Wednesday, down again to 149 pounds on Thursday, and down yet again to 147 pounds on Friday.

It might appear that Sandy has lost 3 pounds in just five days. But let’s see what happens if we use a 3-day moving average instead. Each day, we’d add up that day’s weight plus the previous two days and divide by 3. On Wednesday, Sandy’s 3-day moving average is 149.6. On Thursday, it’s 149.3. On Friday, it’s 149. In other words, her true weight loss is probably closer to one pound!

As you can see, a moving average helps smooth out the daily fluctuations to more accurately reveal the trend. In practice, you’ll probably want to use a larger window to help you focus on the longer-term trends.

Moving averages are used all the time in the real world for a bunch of different things. In fact, there’s so much more to say about this topic that I’m devoting this week’s Math Dude episode to it. So if you’d like to learn more about moving averages, please check it out!


Thanks for your help, Math Dude

So, as Jason explained, charting your weight using a moving average can help reveal your “true” weight and give you a more accurate grasp on the long-term picture: Are you gaining, losing, or maintaining? If your goal is to maintain your weight, I suggest a 15-day moving average. If you are actively working on losing (or gaining) weight, you’ll be able to see your progress more clearly with a 7-day moving average.

If you have a smartphone, there are apps such as True Weight for iPhone that will chart your weight using a moving average. If you don’t have a smartphone, you can use good, old-fashioned pencil and paper or any spreadsheet program. In fact, I used Excel to create the Quick and Dirty Moving Average Calculator. Download it here!

Keep in Touch

Thanks, Jo, for suggesting this week’s episode topic! If you have a suggestion for a future show topic or would like to find out about having me speak at your conference or event, send an email to nutrition@quickanddirtytips.com. You can also post comments and questions  below or on my Nutrition Diva Facebook Page. I answer a lot of listener questions in my free weekly newsletter, so if you’ve sent a question my way, be sure you’re signed up to receive that.

Have a great week and remember to eat something good for me!

Scale image from Shutterstock

About the Author

Monica Reinagel, MS, LD/N, CNS

Monica Reinagel is a board-certified licensed nutritionist, author, and the creator of one of iTunes' most highly ranked health and fitness podcasts. Her advice is regularly featured on the TODAY show, Dr. Oz, NPR, and in the nation's leading newspapers, magazines, and websites. Do you have a nutrition question? Call the Nutrition Diva listener line at 443-961-6206. Your question could be featured on the show.