Calculadora de conceção
The detailed guide below is currently available in English.
Where the 266 days comes from
Clinicians count 40 weeks from the last menstrual period, but conception itself happens about two weeks into that count, at ovulation. That leaves roughly 266 days — 38 weeks — between conception and the due date, and the same span backward from an actual birth date on average. Because a few days of variation is completely normal, the calculator shows a ±3-day window rather than a single certain date.
Why estimates can disagree
Sperm can survive several days before an egg is released, so intercourse date and conception date often differ. Cycles longer or shorter than 28 days shift ovulation similarly, and babies routinely arrive a week or more from their due date. If an exact date matters — paternity timing, genetics counseling, or curiosity — a first-trimester ultrasound is the most reliable evidence. This tool is informational only.
Perguntas frequentes
Is conception the same day we had intercourse?
Not necessarily. The egg is fertilized within about a day of ovulation, but sperm can wait in the reproductive tract for up to five days. Conception therefore usually falls within a few days after intercourse, not exactly on it.
How accurate is a birth-date estimate?
Counting back 266 days assumes the average 38-week gestation from conception. Actual pregnancies range from about 37 to 42 weeks, so a real birth date can sit five weeks from the due date the same math would produce. Use the window, not the single day.