Due Date & Pregnancy Calculator

How the Due Date Calculator works

The calculator uses Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). If your cycle differs from 28 days, the cycle length adjustment corrects the LMP date. If you know your conception date, 266 days (38 weeks) are added instead. The current pregnancy week and trimester are calculated from today's date relative to your LMP.

⚕️ This tool is for informational purposes only. Always confirm your due date with a qualified healthcare professional or ultrasound scan.

Why the Due Date Calculator is Useful

Your estimated due date (EDD) is the single most important reference point in a pregnancy — it anchors every antenatal appointment, every trimester milestone, every piece of medical advice. Knowing it as early as possible lets you plan parental leave, organise prenatal care, prepare the home, and share the news with family at the right time. This calculator supports all three starting points you might know: your last menstrual period (LMP), the date of conception, or a due date provided by a healthcare provider. Beyond just the date, it tells you your current pregnancy week, which trimester you're in, and how many days remain — the full picture from a single calculation.

Key Features

• Three calculation methods: Calculate from your Last Menstrual Period (standard method), a known conception date (adds 266 days), or a due date you already have (works backwards). Each mode shows only the inputs relevant to that method.
• Cycle length adjustment: In LMP mode, you can specify your average cycle length from 21–35 days. For non-28-day cycles, this shifts the estimated due date accordingly — a detail many basic calculators ignore.
• Trimester bar: A colour-coded three-segment bar shows all three trimesters at a glance, with the current one outlined in gold so you can see exactly where you are in the pregnancy arc.
• Four key stats: Current week, trimester number, days remaining to due date, and estimated conception date — all calculated from a single date entry.
• Medical disclaimer: A clearly displayed note reminds users that this is an estimate and that an early ultrasound scan is the most accurate dating method — appropriate for a tool touching a sensitive medical context.

Real-Life Use Cases

• Estimating due date from LMP: Before a first scan, this is often the only calculation available. A quick entry of your last period date gives you a working EDD to share with your GP and use for early planning.
• Verifying a scan-provided date: Use the "Known due date" mode to work backwards and confirm the conception and LMP dates implied by a date your doctor gave you — useful if you're unsure whether the scan adjusted your original estimate.
• Tracking current pregnancy week: Open the calculator at any point during the pregnancy and re-enter your LMP to see what week you're in — helpful between appointments when you want to know where you are without waiting for the next visit.
• Planning parental leave: Many countries require parental leave applications 6–11 weeks before the expected birth. Knowing your EDD early gives you time to check the deadlines and submit paperwork on schedule.
• Sharing milestone information: The trimester and week data gives you precise language for sharing with family, friends, and HR — "I'm in week 14, just into the second trimester" is more informative than a rough date alone.

Who Can Use This Tool

Pregnant women in the early weeks before their first scan who need a working EDD, partners who want to understand the timeline and milestones alongside their partner, grandparents-to-be tracking the weeks, midwifery and nursing students practising obstetric date calculations, and anyone with a known due date who wants to cross-check it, understand current week and trimester, or calculate how much time remains.

Tips & Best Practices

• Always confirm with an ultrasound: Naegele's rule is a statistical average — individual pregnancies vary. An early ultrasound scan (dating scan, ideally between weeks 8–12) is the most accurate way to establish your EDD and should always take precedence over a calculator-based estimate.
• Enter your actual cycle length: If your cycles are consistently 25 or 32 days rather than 28, entering the correct length shifts the estimated due date by several days — which adds up when you're planning appointments and leave.
• Use LMP mode if you don't know your conception date: Most people don't know their exact conception date. LMP is the clinical standard because it's typically a known, memorable date — conception date can only be estimated from it anyway.
• Track the weeks as you go: Revisit the calculator each week to see the progression. Watching "Week 8" become "Week 12" and crossing into the second trimester is a satisfying milestone marker that supports the emotional experience of pregnancy.
• Don't fixate on the exact date: About 95% of babies are not born on their due date. Think of the EDD as the centre of a 2–4 week window. Babies born between 37 and 42 weeks are considered full-term.