This calculator estimates dates from cycle assumptions. It cannot confirm that ovulation occurred, identify safe days for unprotected sex, or diagnose pregnancy. Irregular cycles can make calendar predictions especially uncertain.
Ovulation & Fertility Calculator
Explore calendar estimates from the dates you enter. These estimates do not confirm ovulation, conception or pregnancy.
Enter your cycle details
๐๏ธ Your Cycle Calendar
๐ Cycle Timeline
๐ก General Information
Due date & pregnancy progress
Pregnancy Progress
๐งฎ Conception Date Estimator
๐ฑ Implantation Window
๐ข Cycle Length Calculator
โ ๏ธ Estimated Fertile Days โ Not Contraception
Important: this is not a reliable form of contraception โ even on lower-fertility days pregnancy is possible. For dependable birth control, use a proven method and speak to a doctor.
โ๏ธ BMI & Healthy Pregnancy Weight Gain
โฐ Reminders
Saved on this device only (your browser). Add ovulation, fertility, next-period, medication or appointment reminders.
Disclaimer: This calculator gives estimates based on average cycle data and is for general information and planning only โ it is not medical advice, a diagnosis, or a contraceptive method. Cycles, ovulation and pregnancy vary between individuals. For fertility concerns, contraception, or pregnancy care, please consult a qualified doctor or healthcare professional.
How the calendar estimate is made
For a regular-cycle estimate, the expected next period is the entered first day of the last period plus the cycle length. The estimated ovulation date is that expected period date minus the entered luteal-phase length. The default 14 days is an assumption, not a measurement of your cycle.
For example, a last-period start of 1 September 2026, a 28-day cycle and a 14-day luteal phase imply a next-period estimate of 29 September and an ovulation estimate of 15 September. A different actual cycle length can move both dates. These example dates are arithmetic, not a prediction about a person.
Fertile windows and uncertainty
The NHS menstrual-cycle guide explains that ovulation timing varies and is related to the next period. A calendar cannot observe egg release. Irregular periods, recent hormonal changes, breastfeeding and other factors can make estimates less useful. The displayed window should not be read as a probability of pregnancy on each date.
Using the other tabs
- Due date: a dating estimate, not confirmation of gestational age. Clinical care may establish a different date.
- Conception and implantation: inferred dates cannot identify the date of fertilization, establish paternity or confirm implantation.
- Cycle length: count between the first days of two periods; that describes the recorded interval, not the next one.
- Reminders: browser-local notes are not medical monitoring or guaranteed notifications. Avoid using a shared device for sensitive notes.
What to do with a result
Record actual period dates and compare the assumptions with your own observed pattern. If you need contraception, use an appropriate method rather than the calculator. If you suspect pregnancy, follow pregnancy-test instructions and seek clinical guidance when needed. Persistent cycle changes or fertility concerns deserve a health assessment rather than repeated adjustments until a preferred calendar appears.
Common questions
Does the marked ovulation day mean I ovulated?
No. It is a calculated estimate. The tool does not measure hormones, temperature changes or ultrasound findings.
Can I use it for irregular periods?
You can explore dates from your shortest and longest cycles, but a wider calculated range does not make the prediction reliable. It must not be used to identify safe days.
Does a late period prove pregnancy?
No. A calendar result cannot diagnose pregnancy or its absence. Use a test according to its instructions and consult a clinician for concerns.
Are dates from IVF interchangeable with an LMP date?
No. Select the appropriate method and date type. Your treating clinic’s dating takes precedence.
Related: Irregular-cycle limitations ยท Pregnancy due-date calculator