Pregnancy Due Date Calculator
Due date from last period (LMP) or conception date.
How to use Due Date Calculator
Due Date Calculator: Estimate your pregnancy due date from your last menstrual period or conception date. It is built for speed and privacy: open the page and start, with no account required.
Due Date Calculator is straightforward to use. The output is produced by standard arithmetic applied only to the numbers you type, so it updates the instant you change an input and never depends on a server. Because the work happens locally, there is nothing to install and no waiting on a network.
Open Due Date Calculator on toolpermarket. The tool loads instantly and runs entirely in your browser, so you can begin right away without creating an account.
In the Based on field, pick last period (LMP) or a known conception date. LMP is the most common input.
In the Date field, enter the LMP or conception date. Use the calendar picker for an exact day.
Press Calculate to compute the result. The output appears immediately below the form, and you can change any input and run it again as many times as you like.
Read the result and use it as needed. If anything looks off, double-check your inputs and run it again — the calculation is local and instant, so experimenting costs nothing.
Worked example. An LMP of 2026-01-01 gives an estimated due date of 2026-10-08, which is 40 weeks later.
Tips for accurate results.
Due dates are estimates within about a two-week window.
Conception-based dating skips the uncertain two weeks before ovulation.
Use the LMP unless you know conception exactly.
When to use Due Date Calculator. Estimating when a baby is due. Planning appointments and leave. Converting a known conception date to a due date.
Why use an online calculator tool. A dedicated tool like Due Date Calculator saves the time you would spend opening a spreadsheet, writing a formula, or installing software. It is free, works in any browser, and keeps your input private — handy for a one-off calculation or a quick check while you work.
Everything stays on your device. Due Date Calculator performs no network calls, uploads, or tracking — your input is processed locally and forgotten the moment you close the tab.
Frequently asked questions
How accurate is a due date?
A due date is an estimate, not a precise deadline. Most babies arrive within about two weeks of it. It is computed as 280 days from the last period, which assumes a 28-day cycle and ovulation near day 14.
LMP or conception date — which is better?
LMP is easier to recall and is the standard, but it assumes a regular cycle. If you tracked ovulation or know the conception date, that input can be more precise for you specifically.
Why is it 40 weeks from the last period?
Because pregnancy is counted from the first day of the last period, which is about two weeks before conception. That convention makes the math consistent across clinics even though actual fetal age is roughly 38 weeks.
How accurate is Due Date Calculator?
Due Date Calculator uses the same arithmetic your operating system and spreadsheet use, so the result is as precise as the numbers you enter. It does not round or estimate unless a field is explicitly a rounded display value, and you can recompute any time to double-check.
Is my data sent to a server when I use Due Date Calculator?
No. Due Date Calculator runs completely inside your browser. Anything you type, paste, or upload stays on your device and is never transmitted to a server, stored in a database, or shared with a third party. You can even use it offline once the page has loaded, and closing the tab erases the session.
Does Due Date Calculator work on phones and tablets?
Yes. The layout is fully responsive, so Due Date Calculator behaves the same on a phone, tablet, or desktop — the form reflows to fit the screen and the buttons stay easy to tap. There is no app to install; just open the page in any modern browser and it works.
Is Due Date Calculator free, and do I need an account?
Due Date Calculator is free to use with no account, no sign-up, and no usage limits. It is part of toolpermarket, a matrix of private, browser-based utilities built for everyday tasks, so you can return as often as you like without registering.