This calculator uses Naegele's rule, the standard method providers use: it adds 280 days (40 weeks) to the first day of your last menstrual period. It assumes a regular 28-day cycle, so treat the result as an estimate — only about 1 in 20 babies actually arrives on the due date. Your provider's dating ultrasound is the most accurate source.
Most parents find out the baby's sex at the anatomy scan around 18–20 weeks, so the natural window for a gender reveal party is the few weeks right after — typically weeks 18 to 24. That's late enough to know for sure and early enough that mom is usually feeling good. If you'd rather know sooner, a NIPT blood test can indicate sex from about 10 weeks.
Once you've got your window, Revealcast makes the reveal itself easy: guests guess pink or blue from one link and the answer plays on the big screen for everyone — including family who can't be there. Browse the reveal themes or read up on virtual gender reveal ideas.
The standard method (Naegele's rule) adds 280 days — 40 weeks — to the first day of your last menstrual period, assuming a regular 28-day cycle. A dating ultrasound from your provider is more accurate, especially with irregular cycles.
A NIPT blood test can indicate the baby's sex from about 10 weeks, and the anatomy-scan ultrasound at roughly 18–20 weeks confirms it. That's why most gender reveal parties happen between about 18 and 24 weeks.
It's a solid estimate, but only about 1 in 20 babies is born on the exact due date. Most arrive within a week or two either side. Use it for planning — including picking a gender reveal date — not as a guarantee.