DueDatez is a small, independent project that does one thing: pregnancy date maths, done properly, without getting in your way. Three calculators, no accounts, no newsletter pop-up thirty seconds after you land, and no data leaving your browser.
Why this site exists
Pregnancy calculators are one of the most-searched categories on the web, and most of them are miserable to use. Interstitial ads that cover the result. Trackers firing before the page has even rendered. A "calculator" that turns out to be an email capture form. And underneath all of it, a two-sentence explanation that tells you nothing about where the number came from or how much to trust it.
That last part is what actually bothered us enough to build this. A due date is not a fact, it is an estimate produced by a 200-year-old formula that assumes a 28-day cycle. Roughly one in twenty babies arrives on the calculated date. If a site hands you a date in a big font and says nothing else, it has given you a number without the context needed to read it. We would rather show the working.
What we do differently
- Everything runs in your browser. The calculations are plain JavaScript on the page you are already looking at. Your period dates, cycle length and due date are never transmitted anywhere, because there is nowhere for them to go.
- The maths is adjustable. Most due date tools hard-code a 28-day cycle. Ours lets you enter your real cycle and luteal phase lengths, which can shift the result by several days.
- Every tool is explained. Each page sets out the formula, a worked example, the assumptions behind it and the situations where it will be less accurate. If a tool is unreliable for your circumstances, we say so rather than hiding it.
- No accounts, no email required. There is nothing to sign up for.
- Fast on a phone. Every page is a single self-contained file with no external fonts, frameworks or script libraries. It loads on hospital wifi.
Where our information comes from
The clinical content is written against publicly available professional guidance, principally:
- ACOG Committee Opinion 700 — definitions of term pregnancy (early term, full term, late term, post term)
- ACOG / AIUM / SMFM guidance on methods for estimating the due date and the thresholds for redating from ultrasound
- Published prospective cohort studies of timed intercourse for day-specific conception probabilities
- WHO and CDC public reference material on pregnancy dating and antenatal screening schedules
Guidance changes. Where a figure is a population average rather than a fixed rule, we say which it is. If you spot something out of date or plainly wrong, please tell us — the contact form goes to a real inbox and corrections get priority over everything else.
What we are not
How the site is funded
DueDatez is supported by display advertising. Ads are placed so they do not sit between you and a result, and we do not accept sponsored content, affiliate placements dressed up as recommendations, or paid links in the article text. Nothing you enter into a calculator is used for ad targeting, because none of it is ever transmitted. Our privacy policy sets out exactly what advertising partners can and cannot see.
What is coming next
The tool list is deliberately short. We would rather have three pages that are genuinely thorough than thirty thin ones. Planned additions, in rough order:
- hCG doubling time calculator
- Contraction timer with a 5-1-1 alert
- Pregnancy weight gain ranges by pre-pregnancy BMI
- Corrected age calculator for premature babies
If there is something you keep needing and cannot find a decent version of, tell us. Requests genuinely do shape what gets built.
Get in touch
Corrections, questions, feedback or a request: the contact form, or email hello@duedatez.online. We read everything. We cannot answer medical questions about your own pregnancy — that is not something a website should be doing — but anything about the tools themselves gets a reply.