Marriage is a beautiful thing. Building a life together takes dedication, love and daily vigilance to having each other’s back. That said, one of the other amazing things about marriage is having someone to share your body and heart with. A passionate sexuality, and constantly striving to be each other’s fantasy is a key ingredient to a long-term successful and happy marriage.

While we can talk about how to keep life in the bedroom interesting over time, there is something men may not know about their beautiful bride. Have you ever noticed how her libido ebbs and flows, how some nights she really wants you and some nights, well, she needs extra convincing (or she looks at you like, "You’re kidding, right?"). That’s because her libido is controlled by her hormones, which fluctuate on a daily basis depending on where she is in her menstrual cycle. Would you like to have some fair warning about the changes in her hormone levels? Yeah, we thought so!

Here is a task you can do together that will help both of you have some advanced knowledge about her monthly cycle and how it affects her sex drive. Grab a calendar and a red pencil.

Mark the first day of the wife's period on the calendar as Day 1. Now count out to Day 10 and circle it with your red pencil. On Day 10, she feels great—her estrogen levels are high because her body is getting ready to ovulate, and she’s in the mood for romance. Tonight is about long, slow romantic love making, with candlelight and scented candles. Be sure to nestle her with lots of fluffy pillows, and lift her legs high while rocking her gently and cradling her in your arms.

The next stop on your calendar is Day 14. This is when her egg is ready to drop and her testosterone is spiking, so be prepared. She’s probably feeling sexually aggressive today, and she looks amazing. Other men will flirt with her today too, since she’s giving off an animalistic level of pheromones. If you are trying to get pregnant, this is your perfect day. If not, be sure to take extra care in preventing conception because she is in nature’s perfect moment for propagating the species. Today is a great day for a quickie—she wants you, and she may want you more than once, so be sure to get your beauty rest the night before or catch a nap between sessions! (She will also be almost surely multi-orgasmic today, so be sure to satisfy her any way you can!)

The next day to make note of is Day 18. She wants you, all of you, body and soul. Her body is pumping out a lot of oxytocin—also known as the cuddle hormone and one of our favorite neurochemicals to talk about—so she is really craving your touch. Grab some of your favorite massage oil, a clitoral stimulation gel, and possibly a vibrator, because tonight she will definitely be multi orgasmic. Be sure to touch her a lot everywhere, and you had better clear your schedule because you might be busy for a while…

The last big day to take notice of is Day 28. This is the end of her cycle, so she’s experiencing extra puffiness in her uterus. We find it interesting that in spite of that puffiness, she will get a counterintuitive message from her brain signaling arousal. She’s hot and ready for a very serious climax and she needs it. Now, many of the other articles you will read by us we will be adamant that your woman must climax first for a host of reasons that will intensify and dramatically improve your sex life. That said, tonight on Day 28 of the month, the man comes first. Why? Because her orgasm is going to be huge and hard, and she will want to drift off into what promises to be an amazing night’s sleep.

Our advice is to keep this calendar handy, so you will know best how to please your woman at any time during her cycle. Maybe now that you know more, her monthly period won’t be such an unwelcome visitor, and all the sex you’re having will keep the symptoms of PMS—cramping, bloating and bitchiness—at bay.

Dr. Joni Frater & Esther Lastique are the founders of www.LoveHerRight.com and the authors of "Love Her Right: The Married Man’s Guide to Lesbian Secrets for Great Sex!"