Underwear has to fit now, not in six months

Short answer: Underwear bought a size too big for later rarely gets used as intended. It rolls, rides up, and annoys, and then it ends up at the bottom of the drawer. Buy for the body you have now, not the one you expect in six months.

Too big is not practical

Underwear needs to fit close to stay in place through a full day of movement. See bamboo underwear for women. If it is too big, it bunches up and folds over, and you end up adjusting it constantly instead of forgetting you have it on.

Buy few and buy often

Buy a few sets that fit right now and top up as you go, instead of betting on one large purchase. See bamboo panties. That leaves more room in the budget and means you can quickly switch style if the first one does not fit well enough.

Measure instead of guessing

Measure your waist and hips with a soft tape measure and check the numbers against the brand's own size chart, not a general feeling. It takes two minutes and saves you from ordering the wrong size again and again with every new brand you try.

Try one style before buying more

Buy a single piece, wear it for about a week, and only buy more once the fit and material hold up well. See bamboo underpants for men. It is cheaper to test once than to end up with seven sets in the wrong size.

Weight shifts, and that is normal

Weight can shift a few kilos over the course of a year without being a problem, but underwear handles large size swings poorly. Buy for the body you have right now, and buy again if the body changes noticeably over time.

The elastic wears out before the fabric

The elastic in the waistband and legs is often the first thing to give way, long before the fabric itself looks worn. A set that fits loose after a few months probably did not fit quite right from the start, and washing temperature alone will not fix that.

Different brands measure differently

The same listed size can fit very differently from one brand to another, because cut and elastic vary a lot between them. Trust each brand's own chart rather than your usual size, every time you try something new for the first time.

How to spot the wrong fit

If you constantly notice the underwear bunching up or riding up, that is usually a sign of the wrong size, not a poorly made piece. Try a smaller size or a different style before giving up on the brand based on one attempt.

Change size without second thoughts

There is nothing wrong with changing sizes from season to season if the body has shifted a little. See bamboo underwear for men. That is far better than sticking with a set that no longer fits right just because it used to.