When Can You Find Out the Gender of a Baby?

Pregnancy weeks are counted from the first day of the last menstrual period, not from conception, so the count starts before the baby was conceived. The due date sits 280 days, or 40 weeks, after that first day. The calculator above uses exactly this convention, so if you enter a due date it subtracts 280 days to find the starting point, and if you enter the period date it adds them.

This matters because almost every “when can I find out” answer online is given in weeks, and a mix-up between weeks since conception and weeks since the last period shifts every date by about a fortnight. If your provider has dated the pregnancy from an early scan instead, use the due date they gave you; their dating wins over any calendar sum.

It is easy to think of the mid-pregnancy scan as the reveal appointment, but the sonographer has a long checklist and the sex is not on it as a medical item. The NHS explains that the scan looks for signs of 11 different conditions, checks the baby's growth, and also looks at the placenta and the blood flow in the uterus. Sometimes, it says, the healthcare professional asks another member of the team to check the picture.

That has two practical consequences for anyone hoping to hear “boy” or “girl”. First, the medical checks come first, and the question about the sex usually comes when they are done. Second, the result that matters most from the appointment is the one about the baby's health. The NHS notes that most people are told their baby shows no signs of a condition, and that some are offered further tests. Going in with that in mind keeps the sex in proportion.

Each row in the calculator answers one question: from which calendar day could this option apply to you? The typical week column comes straight from the source named in the last column. The your dates column is our arithmetic, counted from the first day of your last period. A single week such as “from 10 weeks” becomes a start date; a range such as “18–21 weeks” becomes a window that ends on the last day of week 21.

The basis column is the most important one. It tells you whether a row is official guidance (ACOG, the NHS), a research finding (the nub studies) or a company's own claim (the home kits). Those are three different kinds of statement, and we keep them apart on purpose. A date in the table is never an appointment; your provider decides what is offered and when. The copy-link button saves your date in the page address, so you can send the same table to a partner without typing anything again.

Say your due date is May 14, 2027. Subtracting 280 days puts the first day of the last period on August 7, 2026, and every milestone counts forward from there:

Calculated by us from the weeks in the sources above (ACOG, NHS, Efrat et al. 2006 and the kit makers' websites, read October 26, 2026). A week-range ends on its last day, so “21 weeks” runs to 21 weeks and 6 days.

Notice how wide the gap is. Between the earliest blood test a clinic would order and the anatomy scan there are about two months, and for many families that wait is the whole reason the old guessing games exist.

The timing that applies to you depends on where you live, your insurance or health service, and your medical history, so the useful thing to take away from a page like this is a list of questions rather than a plan. These are the ones parents most often wish they had asked earlier:

• Is cell-free DNA screening offered to me, and from which week?
• If I have it, will the report include the sex chromosomes, and can I choose not to be told?
• When will my anatomy scan be booked, and does the clinic tell parents the sex at that scan?
• If I took a home kit, would you want to know the result, and does it change anything you do?
• Is there anything about my pregnancy that changes the usual timing?

Some parents would rather not know until the birth. The NHS describes being asked at the 20-week scan whether you want to know, which is a reminder that hearing the sex is a choice, not part of the test. If a surprise matters to you, it is worth saying so to the team at each appointment.

Before 10 weeks there is no medical test a clinic would offer for this, and before the anatomy scan many families have no answer at all. That gap is where the folklore lives: the ring swinging over the bump, the heart-rate rule, and the oldest calendar of them all, the Chinese gender calendar, which predicts from the mother's lunar age and the lunar month of conception.

None of these can know the answer. A baby's sex is set at fertilization by whether the sperm carries an X or a Y chromosome, and the tests above work because they read that biology directly, either as DNA in the blood or as anatomy on a screen. Folk methods read something else entirely, which is why the one that has been tested on millions of births performed at chance; our Chinese gender calendar accuracy page has the numbers, and old wives tales gender goes through the other tales one by one.

We think the guessing is still worth doing, as long as it stays a game. Write your predictions down before the scan, then score them when the real answer arrives. If you are early on, our early pregnancy gender prediction guide collects the traditions people try in the first trimester, and the Chinese gender chart shows the whole traditional grid.

Diagnostic tests such as chorionic villus sampling and amniocentesis also read the baby's chromosomes, but they are invasive procedures offered for medical reasons, and ACOG describes them as the follow-up to a positive screening result rather than as a way to learn the sex. We leave them out of the calculator on purpose.

We also do not give accuracy figures for the scan or the blood test beyond what the sources above publish, and we do not compare brands or prices. If a number matters to a decision you are making, the person to ask is the clinician who would order the test, because they can tell you how it performs in their lab and for your pregnancy.