Some days you're bigger, some days you're smaller. Diets and the rest of it completely aside, that's just how it is. And in the middle of all the (very important) conversations about self-love and body positivity, people often don't mention this mundane, sometimes frustrating fact.

So it's satisfying to hear someone talk about it normally.

"My weight fluctuates a lot and I move with it. It is what it is," Tracee Ellis Ross says in a recent interview with People. 

"That’s why I try not to have a relationship with the size that I am," the Golden-Globe nominated star of Black-ish adds, sensibly.

A photo posted by Tracee Ellis Ross (@traceeellisross) on Nov 15, 2016 at 5:34pm PST

We hear it all the time: Weight is just a number on the scale, not a concrete indication of your overall health or fitness. Sizes are wildly inconsistent across the fashion industry, so don't freak out if you suddenly seem to have gone up four.

Which is all well and good, until your jeans don't do up. But Ross' answer to this is perfect. "I actually own my favorite jeans in three sizes—28, 29 and 30," she says to People. "Depending on how I feel, I always start with the big ones and if I get to go down, great."

Buying clothes in different sizes shouldn't be about diet "aspirations"—it's a smart, practical way to make sure you always feel good in what you're wearing.

A photo posted by Tracee Ellis Ross (@traceeellisross) on Oct 27, 2016 at 10:09am PDT

"My mom taught me that you can spend money on nice things if you’re going to use them,"  Ellis Ross says. "For example, I have an Alexander McQueen jacket that I wear with everything, even sweatpants.”

(Her mom was music and fashion icon Diana Ross, by the way. Happy to take any advice here.)

"I am not a sample size," Ellis Ross explains. "I am not a model size. I am small for people and big for an actress."

But that's the whole point—changes in size have nothing to to do with your overall "build". They're a normal part of life for women on all ends of the scale.

Even for Chrissy Teigen, who is definitely model size.

“I only shop online basically. Whatever my stylist Monica Rose puts me in, I order it in every color, in usually two different sizes because I fluctuate," she says in her recent cover story for Elle Australia.

And because some days you feel like your shoulderless-peasant-blouse-on-a-beach best self…

A photo posted by chrissy teigen (@chrissyteigen) on Dec 19, 2016 at 9:46am PST

…and others, you just want to wear your jeans and velvet blazer. 

(I don't know, I'm trying. Outside of the "buying clothes in different sizes" thing, it is kind of hard to relate to Chrissy Teigen's life on too many levels.)

A photo posted by chrissy teigen (@chrissyteigen) on Nov 5, 2016 at 6:46pm PDT

The point, which I'm just going to keep on making, is that being aware of the fact you do—and should—change size over the course of a month, makes it way easier to love your body.

Rather than waking up and going, "Oh no, fat day. I'm a monster. 2017 will be different,"Ellis Ross and Teigen's approach is a reminder to say, "Okay, cool. Today is a middle-jeans day."

Why your size changes

A few things come into play here—some can be influenced by diet and exercise, but others are simple biology.

"One day, just to show one of my clients how much weight we typically 'gain' or 'lose' throughout the day, I weighed myself on the hour, every hour," dietician Alexandra Caspero tells Women's Health. "In that one day alone, I fluctuated almost four pounds!"

Water retention and what you eat: "Carbs are not making you fat, but they are affecting water use in metabolism," Caspero says.

This "water weight" is one of the biggest factors in size changes, and is also affected by sodium intake—and how well you're hydrating your body. If you're not giving it enough fluids, it'll try and hold onto it in other ways. It can also be affected by different medications, such as the pill.

If your digestive system isn't working well, you're going to be full of, well, food. And aside from uncomfortable constipation, this causes bloating, and more fluid retention. So keep up the fiber to keep things regular.

Timing: The hormones around your period also play a big part in water retention. You can notice period-related weight gain five to seven days before, dietician Dana Hunnes tells Self, and it will generally get back to normal at around day three or four.

"How big these fluctuations are really depend on the individual, but are usually between two and eight pounds," Amanda Foti, another dietician, tells the magazine.

When you weigh yourself: You might think you're changing size more than you really are, simply because you're weighing yourself at different times on different days. Hunnes says the best time to get your "true weight" is first thing in the morning, naked, just after you've used the bathroom.

Bodies aren't meant to stay the same, we know that. We should dress to celebrate them, not punish them, and build wardrobes that give us room to do it.

Listen to Ellis Ross.

"I want to wear something that makes me feel gorgeous, not that makes me feel self-conscious about my body," she says. "Hiding insecurities or putting attention on the stuff that feels good is really the key."