Letrozole for fertility is commonly taken once daily for 5 days early in the menstrual cycle , most often starting on cycle day 3 or day 5 , depending on the clinic’s protocol. A few fertility guidelines also use day 2 to day 6 or days 3 to 7 , so the exact start day should match your prescriber’s instructions.

Typical timing

  • Day 1 is the first day of full menstrual bleeding.
  • Common regimens include:
    • Days 3–7 for 5 days.
* **Days 2–6** for 5 days.

* Sometimes **day 3 or day 5 starts** are used, depending on the clinic.
  • Ovulation often happens about 5–10 days after the last pill , but this varies.

How people often time sex

Many clinics advise intercourse around the fertile window, often starting a few days before expected ovulation and continuing for several days after, or using ovulation tests/monitoring to narrow the timing. One guideline notes ovulation may occur around days 14–19 with a day 3–7 regimen.

Important safety note

Take letrozole exactly as prescribed by your fertility clinician, because timing can change based on your cycle, diagnosis, and whether your periods are regular. Do not use it without medical supervision, especially if pregnancy is possible or if you have irregular cycles that need monitored timing.

Quick example

If your doctor says “start on day 3 for 5 days,” and your period begins on Monday, then Monday is day 1 , Wednesday is day 3 , and you’d take letrozole Wednesday through Sunday.

Bottom line: the most common answer is start early in the cycle and take it for 5 days , but the exact day depends on your clinic’s plan.