Due date calculator: your delivery date, current week and scan schedule

Work out your due date

The first day of your last period — not the day the bleeding stopped — and your cycle length. Two numbers, nothing else.

What the calculator gives you — and what it doesn't

It gives you three things. First, your estimated delivery date. Second, how many weeks and days along you are today and which trimester that is — the number the hospital asks for at every single visit. Third, the window for the anomaly scan, and the date you reach full term.

What it doesn't give you deserves saying just as plainly. It cannot tell you whether the baby is a boy or a girl — and in India, determining that is a criminal offence under the PCPNDT Act. It cannot predict the baby's weight, whether you'll deliver normally or by caesarean, or whether the pregnancy is going well. None of that follows from a date.

And the most important caveat: the due date is not an exam date. Only about four percent of babies arrive on it. The rest come earlier or later, and that is entirely normal.

How the 40 weeks are counted — you're 'two weeks pregnant' on the day you conceive

Pregnancy weeks are not counted from conception. They are counted from the first day of your last period — which means that on the day you actually conceived, the paperwork already says two weeks.

It feels odd, but the reason is simple. A woman knows the date her period started; nobody knows the exact moment of conception. So doctors the world over count from the date that is known.

One practical consequence: actual gestation is about thirty-eight weeks, not forty. But your file, your scans and your doctor will always speak in the forty-week count — so this tool does too.

Why cycle length can move the date by a week

Most free calculators assume a 28-day cycle and never ask. Real cycles run anywhere from 21 to 35 days, and all of that is normal.

The difference lies in when you ovulate. The egg is released about fourteen days before the next period — however long the cycle. A woman with a 32-day cycle ovulates around day 18, not day 14.

So a cycle four days longer pushes the true due date four days later. With long or irregular cycles, a date calculated from the period alone can be off by a week — and it's exactly those women who end up hearing 'your baby is measuring small' for no reason.

A scan beats any calculation — but only an early one

A scan in the first trimester, ideally between seven and thirteen weeks, is the most accurate way to date a pregnancy. At that stage every baby grows at almost exactly the same rate, so measuring the baby's length gives its age to within five or six days.

If the scan date and the period date disagree by more than a week, doctors adopt the scan date, and it stays. If the date in your file differs from this tool's, that is almost always why.

Later scans cannot re-date a pregnancy. By the third trimester, normal babies vary so much in size that estimating age from measurements can miss by two or three weeks. A late scan checks growth, not dates.

Everything that hangs on this date

The date is not a curiosity — the entire test calendar hangs on it. The NT scan can only be done between 11 and 13 weeks 6 days; done outside that window, it is useless.

The anomaly scan falls between 18 and 22 weeks and is the detailed check of the baby's organs. The glucose test (GTT) comes at 24 to 28 weeks. The tetanus (Td) injections follow the same arithmetic.

So record the date properly — in your phone, not just your memory — and know your current week at every visit. Every decision in that hospital corridor is made against this one number. At government centres, the PMSMA clinic on the 9th of every month offers free antenatal check-ups if you want a second track of care.

The due date is a midpoint, not a deadline

Delivery anywhere between 37 and 42 weeks counts as normal. That is a full month of 'on time' — three weeks before the date to two weeks after.

First babies tend to run late. A due date come and gone means nothing is wrong — though after 41 weeks your doctor will monitor the baby's movements and fluid closely, and will usually discuss induction between 41 and 42 weeks.

A practical tip for the family WhatsApp group: give them 'the last week of the month', not the exact date. Announce a precise date and the daily phone calls start on it — which is the last thing you need in the final days.

Questions

Q: I don't remember my last period date exactly. What now? — Enter your best guess and book a dating scan early. If your cycles are irregular or you recently stopped the pill, the scan is the real anchor.

Q: The calculator's date and my doctor's date differ — which one holds? — The doctor's. It almost certainly comes from a scan, and the scan is more accurate. Every later test is scheduled against that one date, so use it everywhere.

Q: Does this work for twins? — The counting is the same, but twins usually arrive earlier — around 36 to 37 weeks — and your doctor will set a different plan once twins are confirmed.

Q: What if I conceived through IVF? — Then you don't need this tool at all. The embryo transfer date and embryo age are known precisely, so the date your clinic gives you is the most accurate one available.