Frequently asked questions
Short, honest answers to the questions we hear most.
How is my due date calculated?
The most common method counts 280 days (40 weeks) from the first day of your last period. If you know your conception date, we count 266 days from then instead. A dating scan around 12 weeks gives the most accurate estimate, and your midwife may adjust your date after it.
When am I most fertile?
Your fertile window is roughly the five days before ovulation plus the day of ovulation itself, because sperm can survive for several days and the egg is viable for about a day afterwards. Ovulation usually happens around 14 days before your next period, so a longer or shorter cycle shifts it.
My cycle isn't 28 days, does that matter?
Not at all, that's why our ovulation and due-date tools let you set your own cycle length. We assume the luteal phase (ovulation to next period) stays around 14 days and adjust the rest accordingly. If your cycles are irregular, treat the results as a guide and consider ovulation tests or tracking your own signs.
Are these calculators accurate?
They're solid estimates based on typical averages, but every body is different. Cycles vary, ovulation can move, and only about 1 in 20 babies actually arrive on their due date. Use them to plan and understand, and confirm anything important with your GP or midwife.
Do you store my data?
No. Everything runs in your browser. Anything you "save" lives in your own browser's local storage on your device, it never reaches our servers, and there's no account to create.