Estimate your ovulation date and fertile window based on your last menstrual period and cycle length.
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Estimated Ovulation & Conception Date
Thu, July 23, 2026
Ovulation typically occurs around day 14 of your cycle. Most conception happens on the ovulation day, though pregnancy can occur during the entire fertile window.
Fertile WindowSat, July 18, 2026 to Fri, July 24, 2026
Next Period (Approx.)Thu, August 6, 2026
Estimated Due DateThu, April 15, 2027
Days to Ovulation0 from today
This calculator estimates ovulation based on a standard formula (LMP + cycle length – 14 days) and assumes a regular cycle. Actual ovulation timing varies between individuals. For family planning or medical purposes, consult a healthcare provider. Cycle length typically ranges from 21 to 35 days; the average is 28 days.
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What is the Conception Calculator?
A conception calculator is a fertility planning tool that determines your ovulation date and fertile window. It takes your last menstrual period and cycle length as inputs and calculates: the estimated ovulation day (typically 14 days before your next period), the fertile window (5 days before ovulation through 1 day after), the expected date of your next period, and if conception occurs, your estimated due date. It's based on the widely used Naegele formula.
How it works
The calculator works by subtracting 14 days from your cycle length and adding that number to your LMP date. This gives the estimated ovulation day. The fertile window extends 5 days before ovulation (when sperm can survive) through 1 day after ovulation (when the egg is viable). If pregnancy occurs on ovulation day, adding 280 days (40 weeks) to the LMP gives the estimated due date. The next period is predicted by adding your full cycle length to the LMP.
Ovulation Date = LMP + (Cycle Length – 14 days); Fertile Window = Ovulation ± 5 to +1 days; Due Date (if conceived) = LMP + 280 days
Ovulation typically occurs about 14 days before the next menstrual period in a standard cycle. The fertile window accounts for sperm survival (up to 5 days before ovulation) and egg viability (up to 1 day after). If conception happens on ovulation day, pregnancy lasts approximately 280 days from LMP to due date.
Examples
Input
Result
Notes
LMP: 15 June 2026, Cycle: 28 days
Ovulation: 29 June 2026; Fertile Window: 24–30 June; Next Period: 13 July; Due Date: 22 March 2027
A standard 28-day cycle puts ovulation around day 14. The fertile window is 6 days; conception is most likely on the ovulation day itself.
LMP: 1 July 2026, Cycle: 32 days
Ovulation: 19 July 2026; Fertile Window: 14–20 July; Next Period: 2 August; Due Date: 7 April 2027
Longer cycles push ovulation later. Day 18 of a 32-day cycle is when the egg is released; the fertile window is still 6 days before and after.
LMP: 20 May 2026, Cycle: 25 days
Ovulation: 31 May 2026; Fertile Window: 26 May–1 June; Next Period: 14 June; Due Date: 24 February 2027
Shorter cycles mean earlier ovulation. Even with a 25-day cycle, ovulation happens around day 11, and the fertile window is still 6 days.
How to use the Conception Calculator
Enter the first day of your last menstrual period using the date picker.
Enter your typical cycle length (usually 21–35 days; default 28).
The calculator instantly shows your estimated ovulation date.
Note the fertile window—the 6-day window when conception is most likely.
Check your next expected period date and estimated due date (if conception occurs).
Use this information for family planning or to discuss fertility with a healthcare provider.
Benefits
Predicts ovulation day and the full fertile window for family planning.
Accounts for sperm survival and egg viability over multiple days.
Works with any cycle length from 21 to 35+ days.
Provides expected next period and estimated due date for context.
Runs entirely in your browser—no login, no data stored.
Helpful for couples trying to conceive or those tracking fertility.
Tips & common mistakes
Common mistakes
Using the first day of spotting instead of the first full day of menstruation as LMP.
Assuming ovulation happens at the midpoint of the cycle for all women; it depends on cycle length.
Forgetting that cycle lengths vary month to month—use your average if tracking.
Treating the due date as a guarantee rather than an estimate; actual labour occurs within 2 weeks of the predicted date.
Tips
Track your cycle for 3–6 months to find your average length and confirm when ovulation typically occurs.
Combine this calculator with ovulation tests (OPKs) or basal body temperature charting for greater accuracy.
Remember that the fertile window extends 5 days *before* ovulation, not just on the ovulation day itself.
If you have irregular cycles, your ovulation day may vary; consult a fertility specialist for personalised guidance.
Due dates are estimates; only about 5% of babies are born on their due date.
Frequently asked questions
Why do I need to know my cycle length?
Cycle length determines when ovulation occurs. A shorter cycle (e.g., 24 days) means ovulation happens earlier than in a 28-day cycle. Using your actual cycle length makes the prediction accurate to your body.
What if my cycle is irregular?
Use your average cycle length over the last 3–6 months. If cycles vary widely (e.g., 24–35 days), this calculator gives a general estimate. For irregular cycles, tracking ovulation with ovulation tests or temperature is more reliable.
Can I use this if I have PCOS or other fertility conditions?
This calculator assumes regular ovulation. If you have PCOS, irregular cycles, or hormonal conditions, ovulation may be less predictable. Consult a fertility specialist or gynaecologist for personalised guidance.
Is the due date accurate?
The due date (LMP + 280 days) is an estimate. Most babies are born within 2 weeks of the due date. An ultrasound early in pregnancy gives a more precise estimate.
What if I'm not trying to conceive?
This calculator helps identify your fertile window so you can plan around it, whether you're trying to conceive or avoid pregnancy. Combined with barrier methods, it can support contraception planning.
Does this work for everyone?
This calculator works best for people with regular, predictable cycles. Hormonal contraceptives, stress, illness, and cycle irregularities can shift ovulation. Always consult a healthcare provider for medical decisions.