If you’ve been menstruating for the past, say, 15 years, and will continue to do so 12 times a year for an average of 38 years of your life, that’s 456 periods in a lifetime. Theoretically, that should make you a full-blown expert on your period by now. Maybe you’ve mastered the art of not leaking through your clothes since your tween years, thanks to the ability to correctly insert a tampon or just throw on some period underwear  (which unfortunately did not exist when we were younger). Ultimately, we know that getting a monthly period is an important part of reproductive and full-body health — but you may not think as much about the ins and outs of your menstrual cycle from day to day.

Have you ever wondered why your boobs hurt at certain times of the month, or why you’re more tired? Do you know the exact right time to take a pregnancy test? Maybe it’s time to take a step back and look at the big picture — the whole cycle. Most menstrual cycles run for 28 days, with periods lasting about five days. But some people run on a 32-day clock, while others run closer to 21 days, with anywhere between a three-day (lucky!) and a seven-day (sorry) period length. Sometimes the length of your cycle might fluctuate if you tend to have irregular periods.

We encourage you to track your period in your phone’s calendar app or even on a good old fashioned paper calendar. But to gain more insight into what’s going on during each day of your cycle, here’s what you should know about the 28 days.

Phase 1: Menstrual

Day 1: Ready, set, go! The first day of your cycle begins with the day your period starts. The hormone estrogen is at its lowest, and since estrogen is responsible for increasing serotonin (the “feel-good” chemical), you may be feeling pretty lousy today.

Day 2: Gettin’ heavy with it. On average, the second day yields the heaviest flow. But even though you may be at high tide, you may be feeling a bit more relaxed as estrogen levels start climbing again.

Day 3: pH roller coaster. With all those tampons and extra blood flow, your vaginal pH has increased, which can lead to increased susceptibility to yeast infections.

Day 4: Light at the end of the tunnel. Today your period is hopefully getting a bit lighter — the end is near! The number of your scowled looks continues to decrease too as estrogen climbs higher, and we are nice to our partners again.

Day 5: Crossing the finish line. Thank the heavens, and shove your tampons to the back of the cabinet. You won’t be needing those for a while.

Phase 2: Follicular

Day 6: One in 100,000. After your period ends, the most dominant follicle in your ovaries continues to grow in preparation to eventually release an egg.

Day 7: Carpe diem. You should be your normal self now, but possibly a bit more optimistic than usual. You can thank the increasing levels of estrogen for your newly-found motivation to ask for a raise, since studies show that the follicular phase of the menstrual cycle is associated with positive, cheerful emotions with the lift in hormones.

Day 8: Mirror, mirror on the wall. You’re the fairest of them all. Your skin is glowy and bright, you feel good, and you have the confidence to strike up a conversation with that male model at the bar (once again, thanks to that estrogen lift).

Day 9: Making space for a possible baby. While you’re chatting it up with all the cute guys at work, your uterus lining is thickening to make the softest and comfiest bed for your golden egg.

Day 10: Oh, happy day! Every cup is half full, and everything is coming up in roses. Your levels of optimism may be making your friends sick but are making you count every blessing.

Day 11: Let the ovulating begin. Okay, ovulation is just around the corner, and since your ovulation day can change from cycle to cycle, it wouldn’t hurt to start the baby-making process now. That is, if you want a baby — otherwise, it’s a good idea to use birth control or another form of protection.

Day 12: Got that lovin’ feeling. Some say you are possibly your most fertile a couple of days before ovulation, which would make sense that your libido is at an all-time high.

Day 13: Estrogen reaches Mount Everest. Your estrogen levels peak right before ovulation and then drop suddenly right after. So take this as your last day to make lemonade from life’s lemons.

Day 14: Ovulation! The dominant follicle releases the egg for its journey down the fallopian tube. The egg will live for 12 to 24 hours, while sperm can survive three to five days.

Phase 3: Luteal

Day 15: Hello, progesterone. Goodbye, estrogen. Estrogen levels plummet as progesterone levels begin to take its place. You may be a bit irritable, but don’t worry — estrogen will be back soon.

Day 16: It’s getting hot in here. With increased amounts of progesterone, you may notice your body temperature sits a little higher than usual.

Day 17: Don’t take that test quite yet. Anxious to see if you’re pregnant? It might be too early to tell. Hang in there, and check back in next week.

Day 18: Back for round two. Estrogen levels begin to rise again, along with the increasing amounts of progesterone.

Day 19. Easy with the girls. The hormones in your system increase blood flow to your breasts and may cause them to be fuller but extra sensitive.

Day 20: You’re cut off. If your egg hasn’t been fertilized, then your body will call it quits on producing estrogen. Enter: PMS.

Day 21: Baby on board? About ten days after ovulation is when some pregnancy tests may be able to detect faint levels of the pregnancy hormone HCG. If the egg has been fertilized, your hormone levels may be able to accurately answer your pressing “am I pregnant?” question. However, you might be better off to wait until your missed period, which may give you a more accurate test result, according to the Cleveland Clinic.

Day 22: You’re getting sleepy. Today your progesterone levels are at their max, which may equate to an increased tendency to fall asleep in the middle of that super-exciting board meeting.

Day 23: Cool! Small pores. Progesterone activates the production of sebum and swells the skin, causing your pores to appear smaller in size. But the swelling is actually compressing your pores, and the sebum is building up underneath — a situation that may rear its ugly head in a few days’ time.

Day 24: Reschedule your waxing appointment. At this sensitive time of PMS, your body is more susceptible to pain than during other times of the month. Avoid tweezing, waxing or laser hair removal.

Day 25: Let the bloating sink in. You may begin to feel more bloated, no batter what you eat. With all the hormone changes, our bodies tend to hang on to extra water in our system. One of the most ironic cures? Drink more water to flush out your system.

Day 26: Mood swings will happen. You may find that it’s hard to stabilize your mood or that you’re tearing up over puppy videos. This is okay. Feel your feelings. If you find it hard to function in your daily activities or experience debilitating mental stress, speak to your doctor about an evaluation for PMDD, a more severe form of PMS.

Day 27: All the food cravings. As PMS settles in, you will want to eat the craziest combinations of peanut butter and potato chips and chocolate. Give into your cravings, but be mindful to drink plenty of water and not to overdo it with sugar and salt, which can contribute to more bloating.

Day 28: Hi acne, not nice to see you again. What better way to end your cycle than with a visit from the whiteheads? Remember those small pores and sebum production? Well, here’s the result. Additionally, now that your hormones are at an all-time low, your constant testosterone level is actually higher than estrogen and progesterone, causing more stimulation of sebum and a higher chance of cystic acne — not to mention oil-slick skin and large pores.

There are more period products than ever to choose from. Check out some of the coolest options for every kind of menstruator: