Enter the first day of your last period. Adjust cycle length and luteal phase if you track them. We’ll predict ovulation, fertile days, next period, and key testing windows.
Cycles aren’t robots. Ovulation can shift a little from month to month, but there are patterns you can use. This calculator blends your last period date with your average cycle length and luteal phase (the stretch after ovulation) to estimate when the egg is released and which days leading up to it are most fertile. We also outline the predicted next period, a likely implantation window, and two pregnancy test dates—an “earliest try” and a more reliable day—so you can plan without guesswork.
Everything runs in your browser. No sign-ups, no data saved. If you want to share or set reminders, export a calendar (.ics) file or a quick CSV. For broader timing questions, the Pregnancy Due Date Calculator and the Date Calculator are handy companions.
Tip: Pair this with observations like OPKs (ovulation predictor kits), basal body temperature, and cervical mucus—those can tighten the window beyond averages.
Fertile window: Sperm can survive for several days, and the egg is fertilizable for a short period after ovulation. A practical window is ovulation minus 5 days through plus 1 day. That’s why you’ll see several “fertile” boxes, not just one.
Ovulation day: This is a prediction, not a guarantee. It may shift with stress, illness, travel, or just natural cycle variation. If you get a positive OPK, expect ovulation roughly 12–36 hours later.
Implantation window: If conception occurs, implantation commonly begins about 6–10 days after ovulation. Some spotting or mild cramps can occur, or nothing at all—both are normal.
Testing days: An “earliest” test is shown around 9 DPO (days past ovulation), which can catch some early positives. A more reliable day is about 14 DPO, when false negatives are less likely.
Reminder: this is planning information, not medical advice. If cycles are very irregular, absent, or symptomatic, consider chatting with a clinician.
If your cycle length swings a lot, run the calculator with a shorter and a longer value to map a wider target zone. Using OPKs or temperature tracking will give you cycle-specific confirmation.
Only if you’ve tracked it. Many people sit near 14 days. If your luteal phase is shorter or longer, update it so the predicted ovulation lines up better.
Yes. Click “Add to Calendar (ICS)” and open the file with your calendar app. It includes ovulation, the fertile window, and the predicted next period as all-day events.
Because sperm can wait around a bit and the egg remains viable for a short time. The goal is to catch the several days when timing is most favorable, not just the ovulation day itself.
The tool doesn’t diagnose or treat anything; it just does date math from your inputs. If you think you may be pregnant or have concerning symptoms, contact a healthcare professional.