If you have worn a belly band that crept upward all day until it sat somewhere under your bust, you probably concluded the band was badly made. Sometimes it is. More often it is one size too big, and the reason is a completely sensible instinct.
The instinct that causes it
You are pregnant. You are getting bigger. Sizing up feels like the obvious hedge. So you order the next size, and the band arrives with more circumference than your body needs to hold it in place.
A support band works by tension. It needs to be in contact with you along its whole length to stay put. When there is slack, the band has nothing to grip, so every time you sit, stand or bend, it takes the path of least resistance — which is upward, because that is where your body narrows.
What to order instead
Order for the body you have now, not the body you expect in eight weeks. A band built to expand — ours comes in Medium, Large and X-Large with an adjustable closure — has range designed into it. That range is the hedge. You do not need to add a second one on top by sizing up.
Most people land in the right place by choosing based on their pre-pregnancy size rather than their current measurement. If you are genuinely between two sizes, take the smaller one and open the closure, rather than the larger one and cinch it — a band tightened down from too-large bunches at the closure, which is its own kind of uncomfortable.
Three other reasons it might be moving
It is sitting too high to begin with. The band should sit under the bump, not across it. Positioned across the widest part, it has nowhere to go but up.
You are wearing it over a slippery layer. Over a silky camisole or a synthetic base layer, there is very little friction to work with. Directly against skin, or over cotton, it stays put far better.
The elastic has gone. Bands are consumables. If yours has been washed hot or tumble dried repeatedly, the elastic will have given up, and no amount of adjusting brings it back. Cool hand wash, flat dry.
What happens when you sit down for a while
A band that behaves standing up can still ride up after twenty minutes at a desk or in a car seat — sitting changes the geometry the band is working against, folding your torso in a way standing never does. If that's specifically when yours moves, it isn't necessarily a sizing problem: try resting it slightly lower than feels natural while standing, so it has somewhere to settle into once you sit. If it's still climbing within a few minutes of sitting even positioned low, that's usually still the fit — see the full sizing guide for how to check.
When a band is the wrong tool
A support band is a comfort garment. It shares load that would otherwise sit in your lower back, and for a lot of people that is the difference between standing at the kitchen counter for ten minutes and not. It is not a treatment.
If you have pelvic girdle pain, symphysis pubis dysfunction, or any diagnosed condition, the right sequence is to talk to your midwife, physiotherapist or doctor first and let them tell you what kind of support — if any — fits your situation. They may recommend something quite different from a band, and they will be right.
Related reading: How to size a maternity belly band (so it doesn't roll or dig in) · Second trimester bump support: when to start, what actually works