Predicting the best time to have intercourse

Your temperature when you’re fully at rest—called basal body temperature—rises slightly with ovulation. Measuring and recording your basal body temperature over several months can help you predict your most fertile days.

How it works

1. Purchase a special basal body thermometer, available at most drug stores 
2. Record your temperature as soon as you wake each morning 
3. Note when your body temperature rises—this may indicate that ovulation is taking place 
4. Time intercourse with ovulation. Women are most fertile 2 to 3 days before their temperature increases and 12 to 24 hours after

Tips

• It’s important to take your temperature around the same time and under the same conditions each morning. Many factors can influence basal body temperature, including drinking alcohol or smoking cigarettes the night before, a poor night’s sleep, fever, or using the bathroom 
• Because sperm can live for 3 to 5 days inside a woman’s body, having unprotected sex a few days before ovulation could achieve pregnancy 
• Some women don’t experience a change in body temperature at ovulation. For these women, alternative methods will be more helpful 

The calendar method calculates a woman’s most fertile days in the month ahead using the dates of her previous menstrual cycles.

How it works 

1. Circle the first day of your period each month. This is the first day of your cycle
2. After a cycle ends (when your period begins again), record the total number of days in the last cycle
3. Continue to do this for 6 to 12 months
4. To determine your first fertile day:
   - Locate the shortest cycle on your calendar
   - Subtract 18 from your shortest cycle
   - Count ahead that many days in your next cycle, starting with the first day of your period
   - Draw a line through this date
5. To determine the last fertile day:
   - Locate your longest cycle on your calendar
   - Subtract 11 from the number of days in your longest cycle
   - Count ahead that many days in your next cycle, starting with the first day of your period
   - Draw a line through this date
6. The time between the lines is your most fertile window

Tip

• This method may be helpful for women with regular cycles, no matter how long they last 

Hormones that control your menstrual cycle also affect your cervical mucus. Changes in the mucus appearance and consistency can indicate that ovulation is about to begin. 

How it works 

1. Monitor the color and consistency of your cervical mucus each day. Many women have dry days after their period, with white, sticky mucus appearing as an egg starts to mature
2. Record changes on a calendar, labeling the days: “Sticky,” “Dry,” “Wet”
3. Note when mucus increases in volume and becomes clear, slippery, and stretchy, similar to raw egg whites. This is when you’re most fertile

Tips

• Following your period, you’re most fertile at the first sign of wetness or a few days before wetness begins
• This method is less reliable for certain women, including those who are breastfeeding, taking hormonal birth control, using feminine hygiene products, have an infection, or have had cervical surgery