How to Calculate a Pregnancy Due Date by Hand (And Why Your Calculator Agrees)
A step-by-step guide to working out a pregnancy due date with nothing more than a calendar — using Naegele's rule, the LMP method, and the cycle-length adjustment.
The Date Estimator blog
Deep-dives, how-tos and quick tips for everything date-related — pregnancy science, fertility tracking, calendar systems, and the small bits of math that make every calculator on this site work.
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Fertility The Fertile Window, Explained: 6 Days, 1 Egg, and a Lot of Biology
A clear, evidence-grounded explanation of the fertile window, why it's six days long, and how to time it accurately whether you're trying to conceive or trying to avoid it.
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Date math The Surprisingly Tricky Math of Calculating Someone's Exact Age
Why calculating an exact age in years, months and days is harder than it looks — and the rules our age calculator follows to always produce a consistent answer.
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Business What 'Business Days' Really Means in Contracts and SLAs
Counting working days correctly — what counts as a business day, how endpoints are treated, and why holidays vary so widely.
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Calendars A Quick Tour of the World's Calendars (and Why Conversion Matters)
An accessible guide to the Gregorian, Hijri, Hebrew, Persian, Buddhist, Japanese and other major calendars — what they have in common and how they differ.
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Productivity Why Countdown Timers Make You Plan Better (According to Behavioural Science)
How visible countdown timers exploit deadline psychology to improve focus, motivation and follow-through — plus how to use them well.
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Date math Why ISO 8601 Date Format (YYYY-MM-DD) Is Worth the Habit
ISO 8601 sorts naturally, eliminates locale ambiguity and prevents off-by-one bugs. Here's why every date you write should look like 2026-05-06.