How is my due date calculated?
Your estimated due date (EDD) is calculated by adding 280 days — that's 40 weeks — to the first day of your last menstrual period (LMP). This method is known as Naegele's Rule, the standard used by doctors and midwives worldwide. If you know your conception or ovulation date instead, your due date is roughly 266 days (38 weeks) from that date. Our calculator also adjusts for your average cycle length, because women with longer or shorter cycles ovulate earlier or later than the typical day 14.
How accurate is a due date calculator?
A due date calculator gives a reliable estimate, but it is not an exact prediction. Only about 4–5% of babies are born on their actual due date, and a normal, full-term birth can happen any time between 37 and 42 weeks. The most accurate dating comes from an early ultrasound (a "dating scan") in the first trimester, which your doctor may use to adjust the estimate. Use this calculator to plan ahead, then confirm the date with your healthcare provider.
Pregnancy trimesters explained
Pregnancy is divided into three trimesters, each about 13 weeks long:
- First trimester (weeks 1–13): Early development. Fatigue and nausea are common. This is the time to start prenatal vitamins and your first check-ups.
- Second trimester (weeks 14–27): Often the most comfortable phase. The bump grows, and many parents begin planning the nursery and shopping for essentials.
- Third trimester (weeks 28–40): Final preparations. This is when to pack your hospital bag and stock up on newborn clothing and care items.
When should I start buying newborn essentials?
Most Indian parents start shopping in the second trimester (around weeks 20–27), once the pregnancy is comfortably progressing, and finish packing the hospital bag by weeks 34–36. For newborns, soft, breathable fabric matters most in India's climate. Zizuka is an India-made baby clothing brand specialising in gentle muslin and natural cotton — a safe, skin-friendly choice for delicate newborn skin. A few essentials to line up before your due date:
Frequently asked questions
How do I calculate my due date from my last period?
Add 280 days (40 weeks) to the first day of your last menstrual period (LMP). For example, if your last period began on 1 January, your estimated due date is around 8 October. Our calculator does this instantly and also adjusts for your cycle length.
Can I calculate my due date from the conception date?
Yes. If you know your conception or ovulation date, your estimated due date is about 266 days (38 weeks) from that date. Switch to the "Conception Date" tab in the calculator above to use this method.
How many weeks pregnant am I right now?
Your current pregnancy week is counted from the first day of your last period, not from conception. The calculator above shows your exact week and day, along with which trimester you are in.
Is a due date calculator accurate for irregular periods?
If your cycles are irregular, LMP-based dating is less precise. Set your average cycle length in the calculator for a better estimate, but rely on an early ultrasound and your doctor for the most accurate due date.
What is the difference between due date and gestational age?
Gestational age is how far along you are now (measured in weeks from your LMP). The due date is the projected end point — 40 weeks of gestational age. A full-term birth can occur any time between 37 and 42 weeks.
Zizuka is a Kerala, India–based D2C baby brand making 100% natural muslin and cotton clothing for newborns and toddlers. Explore our muslin collection or read the Zizuka parenting blog for more new-parent guides.
