Health & Fitness
Pregnancy Due Date Calculator
Pregnancy Due Date Calculator is a browser-based calculator tool on CalcToolsBase. Estimate your due date from your last menstrual period, adjusted for your cycle length. To use it, enter your values and view the result directly in your browser — no signup and nothing to install.
Want to track the key dates of a pregnancy? Pregnancy Due Date Calculator does it from your first day of last menstrual period and average cycle length and shows the due date and how far along you are clearly, with everything calculated in your browser.
About this calculator
Pregnancy Due Date Calculator is built to track the key dates of a pregnancy without a server round-trip. Provide your first day of last menstrual period and average cycle length and it uses standard 280-day dating to produce the due date and how far along you are, instantly and entirely in your browser, which makes it handy for quick checks and repeat runs.
A due date is an estimate; only about one in twenty babies arrives on the exact date. Ultrasound dating and your healthcare provider are more reliable than any calendar formula.
How to use
- Enter the first day of your last menstrual period (LMP).
- Enter your average cycle length in days.
- Press Calculate to see your estimated due date.
- Confirm the dating with your healthcare provider.
Why use Pregnancy Due Date Calculator
Fast
Calculations run in your browser. No round trip to a server.
Private
Your inputs never leave your device. Nothing is uploaded.
Free
No signup, no paywall, no ads-in-results, no watermarks.
Educational
Uses common calendar-based estimates for educational purposes only. Confirm medical questions with a qualified professional.
Mobile-ready
Optimised for phones, tablets, and desktops alike.
Transparent
Clear about the method used and its limits, with disclaimers where they matter.
Common uses
Pregnancy Due Date for tracking a pregnancy week by week
Pregnancy Due Date for planning antenatal appointments
Pregnancy Due Date as a general guide between scans
Pregnancy Due Date for maternity-leave planning
Pregnancy Due Date when sharing the news with family
Pregnancy Due Date when noting key pregnancy milestones
Technical notes
Pregnancy Due Date Calculator estimates the due date with Naegele's rule — first day of the last period plus 280 days (40 weeks) — and counts gestational age from it.
These are general-population estimates and not a substitute for advice from a qualified clinician.
Because it runs locally, results appear instantly with no server round-trip.
FAQ
Does cycle length change the due date?
Yes. This tool adds the difference between your cycle and 28 days to the standard 280-day estimate, so a 35-day cycle pushes the due date about a week later.
How accurate is a calculated due date?
It is an estimate. Roughly 1 in 20 births occur on the exact predicted day, and ultrasound dating is generally more accurate than an LMP-based calculation.
Can I use this if my cycles are irregular?
With irregular cycles an LMP-based estimate is less reliable. Treat the result as a rough guide and rely on ultrasound dating from your provider.
Does the Pregnancy Due Date Calculator send my data to a server?
No. The Pregnancy Due Date Calculator runs entirely in your browser — your inputs never leave your device, and nothing is uploaded or stored.
Worked example
By Naegele's rule, the due date is the last menstrual period + 280 days (40 weeks). An LMP of 1 Jan gives a due date around 8 October.