There are certain things that are best at specific times of the day. Coffee is best in the morning; a scary movie right before bed is not. (Meanwhile, breakfast is suitable at literally any hour.) However, if you’ve recently started a vitamin-taking kick ~for your health~ you might be looking at all of those supplements lined up before you and wonder if there’s an optimal time to take them.

Let’s be real: The best time to pop a pill is whenever you’ll remember. “If you’re not consistently going to take your vitamin, you’re getting less of it over the course of the week,” says Christy Brissette, President of 80 Twenty Nutrition—and less is always less.

That said, there are some differences between how certain vitamins are processed by your body, so timing can sometimes make a difference. While your body can absorb water-soluble vitamins, like B and C, no matter what you have or haven’t eaten, other supplements are best taken with food, while others don’t mix well with certain vitamins. Here’s what you need to know about when to take vitamins, no matter your unique supplement mix.

Fat-soluble vitamins: at mealtime

Your body better absorbs fat-soluble vitamins (A, D, E, and K) when they’re taken with fat-containing food. That’s because eating fat triggers the production of enzymes and bile that help transport fat-soluble nutrients out of your digestive system and into your liver, where they’re processed. “Without that activation, you won’t absorb as much of those vitamins as effectively,” says Brissette. Don’t take this as carte blanche to dive into a triple-cheese pizza for the sake of getting more vitamin D. Brissette says even 5 grams of fat is enough to get that effect—think toast with mashed avocado or oatmeal with sliced almonds.

Since multivitamins and prenatals contain fat-soluble vitamins, they’re also best taken at mealtime, Brissette adds.

Vitamin B: with breakfast

If you’re taking a B vitamin—or a multi or prenatal containing B—you might find you need to take it earlier in the day. “B vitamins boost your energy levels, so some people find if they take it at night or with a late dinner it’s a bit too stimulating. But it doesn’t bother other people,” says Brissette. If you can never remember to take your pill in the morning, or if taking a prenatal during the day makes nausea worse, it’s perfectly fine to take it later in the day.

Calcium: separately from iron and zinc

If you’re taking calcium as well as iron or zinc, space your supplements throughout the day. Calcium competes for the same resources as zinc and as iron, so “they’ll duke it out in your body,” says Brissette. Mayo Clinic suggests aiming to leave at least one to two hours between vitamins. “I usually tell people to take them at a separate meal,” says Brissette.

Also keep in mind that your body can only absorb 600 mg of calcium at a time—so if you’re taking more, have one dose in the morning and one in the evening. “Otherwise you’re flushing anything over 600 mg down the drain,” notes Brissette.

Iron and magnesium: with dinner

Iron can cause upset stomach, while magnesium can have a laxative effect that’s less than ideal in the middle of your workday. Caffeine also reduces the amount of iron your body is able to absorb, notes the NIH, making it a bad pair with your morning matcha latte. So take both iron and magnesium with a meal, preferably dinner, to slow down the digestive process and reduce the chance that they’ll irritate your stomach. “Anytime you think a supplement might be causing upset stomach, having it with food or later on in the day can be easier than on an empty stomach,” says Brissette.

Fiber: right before bed

The megadose of fiber in a supplement can interfere with the absorption of medications and other nutrients, so take it separately from your prescriptions, meals, and other vitamins. “The best time is with a big glass of water before you go to bed,” says Brissette.

Other vitamin timing FAQs

FYI: Certain vitamins work better together. Vitamin D and magnesium help your body absorb calcium—which is why you’ll often see the three paired in the same pill. Vitamin B12 and vitamin C help your body process folic acid, while vitamin C also improves iron absorption. “That’s especially important for vegetarians, because the iron in plant-based foods is absorbed only half as well as iron found in meat, fish, and poultry,” says Brissette. The vitamins in foods count, too—so consider downing your iron supplement with a glass of vitamin C-rich OJ.

Brissette adds that some prenatals and multis require you to take two or three pills—and you can’t just swallow all three at once and be done with it. “The reason they’re separated is because it’s meant to be taken at different times of the day,” she says. If remembering to take a supplement multiple times a day sounds daunting, you may want to opt for a vitamin that contains a full day’s dose in one capsule. And if you’re looking to keep things simple (which, understandable!)…a one-a-day multi might be your best bet.

Looking for more vitamin FAQ? Here’s the deets on whether or not they expire. And here’s how to shop for a vitamin to ensure you’re not accidentally getting fillers and shady ingredients.