Handy tools
Ovulation Calculator
Enter your last period and cycle length to get your ovulation day, fertile window, next period and due date at once!
Enter the first day of your last period and your average cycle length, and we'll estimate your ovulation day, fertile window, next period, and pregnancy due date — all at once.
Usually 21–35 days (default 28). Use your average over the last few cycles.
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The Giggleus Ovulation Calculator needs two inputs — the first day of your last period and your average cycle length (21–35 days) — and shows your estimated ovulation day, fertile window, next period and the due date if you conceive this cycle, all on one screen. Everything runs in your browser; nothing is sent to a server.
How it works: ovulation is placed 14 days before your next expected period, so a 28-day cycle gives day 14 and a 32-day cycle gives day 18. The fertile window runs from five days before ovulation to one day after, because sperm can survive several days and the egg about a day. The due date follows Naegele's rule (last period + 280 days), shifted by however much your cycle differs from 28 days. These are calendar estimates for a regular cycle: they can't confirm ovulation, don't guarantee pregnancy and are not a method of contraception.
Frequently Asked Questions
Q. How does the calculator work out my ovulation day?
A. It counts back 14 days from your next expected period (last period + cycle length). For a 28-day cycle that's day 14; for a 32-day cycle, day 18. The fertile window is the five days before ovulation plus the day after.
Q. Can I use this ovulation calculator to avoid pregnancy?
A. No. A calendar estimate is not birth control — ovulation can shift from cycle to cycle even when periods are regular, so 'safe days' worked out this way are unreliable. Ask a doctor or pharmacist about a contraceptive method that suits you.
Q. Is it accurate if my cycle is irregular?
A. Not really. The calculation assumes the same cycle length every month, and only 21–35 days can be entered. If your cycle often falls outside that range, changes a lot from month to month, or comes with severe pain or very heavy bleeding, see a gynecologist; ovulation test kits or basal body temperature tracking give more direct signs.
Q. How is the due date calculated?
A. With Naegele's rule: first day of your last period + 280 days (40 weeks), adjusted by the difference between your cycle and 28 days. Your doctor will confirm or update it with an early ultrasound.