Use this calculator to estimate when you’re most likely to ovulate after a cycle of Clomid (clomiphene) or Letrozole. Enter your regimen and last pill date to get a likely ovulation window, the earliest reliable test day, and an estimated due date if you conceive. Educational only—timing varies and clinical monitoring is best.
Methodology and Sources
What this estimates
This tool estimates an ovulation window after a standard 5 day course of clomiphene citrate or letrozole, suggests earliest reasonable home pregnancy test timing, and provides an estimated due date if conception occurs. It is educational and not a diagnosis.
Dosing patterns used
Typical induction regimens are clomiphene 50 to 150 mg daily or letrozole 2.5 to 7.5 mg daily for 5 consecutive days (often cycle days 3 to 7 or 5 to 9). These schedules reflect common practice in guidelines for unexplained infertility and ovulation induction.
Sources: ASRM guideline on evidence based treatments for unexplained infertility (2020) and ESHRE guideline on unexplained infertility (2023). ASRM 2020 ESHRE 2023
Ovulation after last pill
Clomiphene: Ovulation usually occurs about 5 to 10 days after completing a clomiphene course. The calculator centers the window in that range and widens it slightly for higher or repeat dosing.
Reference: Drugs.com professional monograph (states ovulation usually occurs 5 to 10 days after a course).
Letrozole: Clinical handouts commonly advise that ovulation occurs roughly 5 to 8 days after the last tablet. The calculator centers the window in that range and allows modest variability by dose and cycle day of the course.
Reference: clinic instruction sheet noting ovulation 5 to 8 days after last letrozole tablet Coastal Women’s Healthcare handout.
Additional timing context for clomiphene intercourse start around day 10 is noted in UK NHS trust leaflets, for example Ashford and St Peter’s Hospitals leaflet.
Earliest reasonable test timing
Over the counter tests are most reliable on or after the expected period. For early testing, many patients use 10 to 12 days after the estimated ovulation day as a first try, with repeat testing 48 hours later if negative.
Reference: ACOG patient education notes home tests are most accurate after a missed period. ACOG patient FAQs.
Due date calculation
If conception is assumed, the estimated due date is calculated as ovulation date plus 266 days, which corresponds to last menstrual period plus 280 days in standard obstetric dating.
Reference: Methods for estimating the due date (ACOG, AIUM, SMFM consensus summarized here) Committee opinion summary.
Why clomiphene and letrozole differ
Clomiphene is a selective estrogen receptor modulator with a longer half life and antiestrogenic endometrial effects in some cycles. Letrozole is an aromatase inhibitor with a shorter half life and is widely used off label for ovulation induction. Both are first line options in many guidelines, and head to head trials inform effectiveness rather than exact ovulation day.
Reference: AMIGOS randomized trial of letrozole versus clomiphene with IUI in unexplained infertility NEJM 2015.
Safety and limits
The tool does not replace ultrasound or laboratory monitoring. Multiple gestation risk rises with higher response, especially with gonadotropins, and programs individualize dosing to reduce risk.
References: ASRM Committee Opinion on multiple gestation 2022. General practice context: ESHRE 2023.
Limitations
Ovulation timing can vary by dose, cycle day of start, diagnosis, luteinizing hormone surge behavior, and individual pharmacokinetics. The calculator uses population averages and conservative windows. Follow your clinic’s instructions for monitoring, trigger timing, and intercourse or IUI timing.
How timing typically works
Protocols vary, but many cycles follow these patterns from the last pill day (LPD):
| Medication | Common regimens | Likely ovulation after LPD |
|---|---|---|
| Clomid (clomiphene) | Days 3–7 or 5–9 | ~5–10 days after LPD is typical; some ovulate sooner/later. |
| Letrozole (Femara) | Days 3–7 or 5–9 | ~5–8 days after LPD for many; range can extend to ~10. |
Tips to improve timing
- OPKs work on both meds for most users; consider testing 1–2×/day as you approach the window.
- If you use an hCG trigger, ovulation commonly occurs about 24–36 hours later. Follow your clinician’s timing for intercourse/IUI.
- Timed intercourse: every 1–2 days during and just after the predicted window works well for most couples.
Educational only. If you’re not seeing ovulation by OPK/ultrasound or your cycles are irregular, ask your clinician about monitoring or dose adjustments.
Clomid/Letrozole FAQs
When should I take a pregnancy test? â–ľ
Most people can test reliably about 14 days after likely ovulation. If you used an hCG trigger, wait the number of days your clinic recommends (often 10–14 days) to avoid a false positive.
Do OPKs work while on Clomid or Letrozole? â–ľ
Yes—OPKs detect the LH surge that precedes ovulation. Clomid can occasionally cause earlier/larger LH fluctuations; testing daily (or twice daily near your window) improves detection.
What if I don’t ovulate within the window? ▾
It happens. Talk with your clinician about ultrasound monitoring, adjusting dose/days, adding a trigger, or switching medications.
Does dose (e.g., 2.5 vs 5 mg Letrozole) change timing? â–ľ
Timing is similar across common doses; the bigger effect is on whether ovulation happens at all. Your exact day can still vary cycle to cycle.
Can I time intercourse or IUI without ultrasound? â–ľ
You can use this calculator + OPKs as a guide, but ultrasound is the gold standard for follicles and lining. For IUIs, follow your clinic’s protocol.
What’s next?
On a trigger? Follow your clinic’s timing. If you’re doing IUI, confirm the schedule they gave you.