Cycle day one is the first day of bleeding
Period predictions start with the first day of menstrual bleeding and add an average cycle length. A single cycle may not represent a usual pattern.
Ovulation is a calendar estimate
ToolBullet estimates ovulation 14 days before the next expected period. Actual timing can shift, and a calendar cannot confirm that ovulation occurred.
The fertile window extends beyond one day
The calculator displays five days before estimated ovulation through one day after. This reflects the period in which pregnancy may occur, but it cannot identify guaranteed fertile or non-fertile days.
Pregnancy dates use gestational conventions
An estimated due date is 280 days from the first day of the last menstrual period or 266 days from conception. Clinical gestational age is conventionally counted from about 14 days before conception.
Term categories are distinct
Early term begins at 37 weeks. Full term begins at 39 weeks. A calculator cannot predict the actual date of labour, and clinical dating may revise the estimate.
Important limitations
- Irregular cycles reduce calendar reliability.
- Hormonal contraception, breastfeeding, illness and perimenopause can alter timing.
- These tools do not confirm pregnancy, ovulation or fertility.
- Calendar estimates should not be the sole method used to prevent pregnancy.