Implantation Window Calculator
The implantation window is the brief period when the uterine lining becomes receptive to implantation of a fertilised egg. Understanding when this occurs can help you identify symptoms of early pregnancy, time a pregnancy test correctly, and understand your reproductive cycle. Implantation typically takes place 6-12 days after ovulation, most commonly around 8-10 days post-ovulation. Since ovulation in a 28-day cycle typically occurs around day 14, implantation usually happens between days 20-26 of the cycle. This calculator takes your last menstrual period date and cycle length to estimate your ovulation date and your expected implantation window.
Implantation window calculation
Ovulation date = LMP + (Cycle length - 14) days
Implantation window = Ovulation + 6 days to Ovulation + 12 days
Earliest reliable test = Ovulation + 14 days (14 days post-ovulation)
Implantation: frequently asked questions
What is the implantation window?
The implantation window is the period during the menstrual cycle when the uterine lining (endometrium) is receptive to a fertilised egg (blastocyst). It typically occurs 20-24 days after the last menstrual period, or 6-10 days after ovulation. Implantation triggers early pregnancy and hCG hormone production.
How long does implantation take?
After fertilisation, the embryo travels down the fallopian tube for 6-12 days before implanting in the endometrium. Implantation itself takes 1-3 days. Early (before day 8 post-ovulation), average (days 8-10), and late (days 10-12) implantation all result in viable pregnancies.
What is implantation bleeding?
Light spotting or pinkish discharge that occurs when the embryo burrows into the uterine lining is called implantation bleeding. It occurs in about 15-25% of pregnant women and typically happens around days 24-28 of a 28-day cycle. It is much lighter than a menstrual period and lasts 1-2 days.
When can I take a pregnancy test after implantation?
hCG (the pregnancy hormone) starts to be produced after implantation. It takes 1-2 days after implantation for hCG to enter the bloodstream and then urine. Most home pregnancy tests can detect hCG 10-14 days after ovulation (or 1-2 days after a missed period). Testing too early increases the chance of a false negative.
What cycle length should I use if my cycle is irregular?
Use your average cycle length based on several recent cycles. Ovulation typically occurs about 14 days before the next expected period, not 14 days after the LMP. If your cycle is 32 days, ovulation is roughly on day 18, not day 14. An irregular cycle makes prediction less precise; tracking basal body temperature or using ovulation tests helps.
Official sources
- National Institute of Child Health and Human Development: Preconception Health.
- American College of Obstetricians and Gynecologists: Calculating Your Due Date.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.