Pregnancy Due Date Calculator

About the Pregnancy Due Date Calculator

Estimate a baby's due date using Naegele's rule — 280 days from the first day of the last menstrual period — adjusted for cycles longer or shorter than 28 days. You'll also see how many weeks and days along the pregnancy is today and which trimester it's in.

How to use it

1. Enter the first day of the last period.
2. Adjust the average cycle length if it isn't 28 days.
3. Read the estimated due date and current week.

Tips and good to know

• Only about 4% of babies arrive on their due date; most come within two weeks either side.
• Pregnancy weeks are counted from the last period, about two weeks before conception.
• An early ultrasound usually gives the most accurate dating.
• This is an estimate, not medical advice — always follow your healthcare provider.

About everyday tools

Some questions come up again and again: how old is someone exactly, how many days until a deadline, what day of the week was a date. They are easy to get slightly wrong by hand because months have different lengths and leap years move the goalposts.

These helpers use your browser's own calendar maths, which follows the Gregorian calendar used internationally. They are quick, precise and private — handy for forms, planning and settling friendly arguments.

Date arithmetic is a classic source of off-by-one errors. A 'month' can be 28, 29, 30 or 31 days long, a year can be 365 or 366 days, and people born on 29 February have a birthday that only appears every four years. These tools count calendar months first and then the remaining days, which matches how ages are written on official forms. Everything runs on your device, so no dates of birth or personal details are ever stored or transmitted. If you need an age for a legal purpose, check the specific rule used by the organisation asking, as a few jurisdictions count differently.

The unit converters use the exact international definitions agreed in 1959 — one inch is exactly 2.54 centimetres and one pound is exactly 0.45359237 kilograms — so results match engineering references rather than rounded rules of thumb. Health figures such as BMI follow published World Health Organization thresholds and are offered as general information only, never as a diagnosis. Random numbers come from the cryptographic generator built into your browser, the same source used to create secure keys, which makes draws genuinely unpredictable and fair.

Popular ways people use everyday tools

• Confirming an exact age for school enrolment, sports categories, insurance or benefits forms.
• Counting the days left until a birthday, anniversary, deadline or long-awaited trip.
• Working out how old someone was on a particular historical date for family research.
• Settling friendly arguments about who in the family is older and by exactly how many days.
• Converting recipe weights, oven temperatures and luggage limits when travelling between metric and imperial countries.
• Planning milestone celebrations such as a 10,000th day alive or a fortieth birthday.

How we build and test our free tools

Every tool in this collection is built and tested by The Curator team. Before a tool is published we check it against known reference results — textbook loan schedules, standard test vectors for hashes, sample files for conversions — and we re-check it whenever browsers change. Each page explains the method so you can verify the answer yourself rather than take it on trust.

The tools run as JavaScript inside your browser tab. When you choose a file, your browser reads it from your disk into memory; the tool processes it and gives you the result as a download. No copy is sent to us or to anyone else, and nothing is kept after you close the tab. That is why these tools are safe for personal documents, and why they keep working on a slow or interrupted connection once the page has loaded.

The collection is free because it is supported by advertising on these guide pages. We never charge for a tool, never add watermarks and never sell what you type. If something doesn't work as described, or you would like a tool we don't have yet, please contact us — new tools are added in regular batches based on what readers ask for.

Frequently asked questions

Why adjust for cycle length?

Ovulation happens later in longer cycles, so the due date moves later by the same number of days.

Is anything saved?

No — dates stay in your browser.

Which trimester boundaries are used?

First up to 13 weeks 6 days, second to 27 weeks 6 days, third after.

Is the Pregnancy Due Date Calculator really free?

Yes. There is no account, no trial and no watermark. The Curator is supported by advertising on its guide pages, never by charging for tools or selling your data.

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