Pregnancy Check Calculator

Days from ovulation to the next period. Stable for most people at 12-14 days; a home progesterone or LH record gives yours.
Only used to count the days from now to each testing date.
First day of a missed period
2025-03-30
When To Take a Pregnancy Test Calculator
Earliest an early-result test is labelled for
2025-03-24
A negative becomes trustworthy
2025-04-06
Estimated ovulation
2025-03-15
Period due
2025-03-29
Implantation window opens
2025-03-21
Implantation window closes
2025-03-27
Days until the earliest test date
-539
Days until the missed period
-533
Pregnancies implanted by the missed period
90 %
Pregnancies implanted a week later
97 %
Dated from
Last menstrual period with a 28-day cycle
Where today sits
More than a week past the missed period. About 97% of pregnancies have implanted by now, so a negative test with no period is worth taking to a clinician.
Worked out from Wilcox AJ, Baird DD, Weinberg CR. Time of implantation of the conceptus and loss of pregnancy and 2 other sources.
These dates assume ovulation happened when the cycle arithmetic says it did. Cycles vary, and a late ovulation moves every date here later - which is the single commonest reason for an unexpected negative.
Use first-morning urine for the earliest tests; hCG is most concentrated then, and drinking a lot beforehand dilutes it.
An estimate from calendar arithmetic, not a clinical assessment. Only about 4% of births occur on the estimated due date; ultrasound dating by a clinician supersedes menstrual dating when they disagree. A negative test before the missed period means very little - about 10% of pregnancies have not implanted by then and cannot yet be detected by any test. Confirm any positive with a clinician, and seek urgent care for severe one-sided pain or heavy bleeding, which can signal an ectopic pregnancy.

How this is worked out

6 steps
  1. Ovulation is one luteal phase before the next period, so on cycle day 28 - 14 = 14: 2025-03-15.
  2. The next period is due 28 days after the last one started: 2025-03-29.
  3. Implantation happens 6 to 12 days after ovulation, so between 2025-03-21 and 2025-03-27.
  4. The earliest day an "early result" test is labelled for is 5 days before the period is due: 2025-03-24.
  5. A missed period starts the day after it was due: 2025-03-30. By then implantation has happened in 90% of pregnancies.
  6. One week later, 2025-04-06, that has risen to 97%, which is when a negative test is worth believing.
Day-by-daytable
dateweekdaymilestonedetection
2025-03-24Monday5 days before the period is due>=76%
2025-03-25Tuesday4 days before the period is due96%
2025-03-26Wednesday3 days before the period is due>99%
2025-03-27Thursday2 days before the period is due>99%
2025-03-28Friday1 day before the period is due>99%
2025-03-29SaturdayThe day the period is due>99% of samples from pregnant women, per the package insert
2025-03-30SundayFirst day of a missed period90% of pregnancies have implanted by now (Wilcox 2001)
2025-04-06SundayOne week after the missed period97% have implanted; a negative here is meaningful (Wilcox 2001)

Results are general information, not financial, tax, legal, medical or engineering advice.