Get one with a built-in liner and quick-dry fabric.

That’s it. A swim dress without a liner isn’t a swim dress — it’s a beach cover-up that will embarrass you the first time you get out of the water. Quick-dry fabric matters because wet cotton clinging to you in the sun is miserable and slow to dry.

Don’t overthink the modest part. Most swim dresses are modest by design: knee-length or longer, often with a skirt cut, sometimes with sleeves. The real decision is where the sun comes from. If you’re fair-skinned, get one with UPF 50+ fabric. If you burn easily, also look for a higher neckline and longer sleeves.

Avoid anything that floats up when you swim. The skirt should be heavy enough to stay down, or lined so it sinks. A few brands make swim dresses with a built-in shorts layer underneath — those are great if you plan to chase kids in the waves.

You don’t need to spend $100. Target’s swim line has solid options. Land’s End does too, and their sizing is consistent. Don’t order anything that can’t be returned easily.

Your only job is to make sure it feels good wet. Everything else is preference.