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Implantation Calculator

Date the 6-to-12-day implantation window from your last period or a known ovulation date, with the peak days, the earliest reliable test date and the expected period.

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Open Implantation Calculator and you get an answer straight away, with no account to create. Its place is under Pregnancy & baby; Baby Growth Percentile Calculator and Baby Milk Intake Calculator answer the questions closest to this one.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What does Implantation Calculator do?

Date the 6-to-12-day implantation window from your last period or a known ovulation date, with the peak days, the earliest reliable test date and the expected period.

When would I actually use this?

Placing a pregnancy on the calendar: the estimated due date, the current week, and when the usual appointments and screenings fall.

What is the most common mistake?

Reading the due date as a deadline. It is a median: fewer than one birth in twenty happens on it, and a normal term spans several weeks around it.

Is there a tool for the next step?

Baby Milk Intake Calculator is the closest one after this: Bottle volumes per feed and per day by your baby's weight and age, with the feeding interval.

What else is worth having open alongside it?

Gestational Age Calculator and hCG Doubling Time Calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

Dating follows Naegele's rule (280 days from the last period) or the transfer date for assisted conception. An early ultrasound is more accurate than any calculation and takes precedence over it.

Further reading

All guides →
ExplainerImplantation Timing and the Window That Decides a Test ResultHow early you can test is the sum of three delays: when implantation happens, how fast hCG climbs from that moment, and what the test can detect. Each one is measured in the literature, so the chain can be computed end to end — and it explains exactly why an early negative is so often wrong.ExplainerIVF Dating Is the One Case Where the Date Is Actually KnownEvery other pregnancy is dated from an estimate. After IVF, fertilisation is timed to the hour, so gestational age is arithmetic: 266 days from fertilisation, minus the embryo's age at transfer. Here is the derivation for day-3, day-5 and day-6 embryos, why frozen and fresh transfers use the same rule, why an early scan rarely moves an IVF date, and what the two-week offset on a scan report means.ExplainerhCG Doubling Time, and What a Single Number Cannot Tell YouDoubling time is ln(2) times the interval divided by the natural log of the ratio. Here it is derived and worked on real pairs, with the two things most often got wrong online: the expected rate slows as the level rises, and a single value is meaningless because the reference range at one gestational week can span more than two hundredfold.ExplainerCycle Length, Ovulation, and What a Fertile Window Really IsOvulation is estimated far better by counting backwards from the next period than forwards from the last one, because the phase after ovulation is the stable one. Here is the inversion worked for every cycle length, the fertile window from the study that defined it, and the failure rates that make this unusable as contraception.ExplainerHow Pregnancy Dating Actually WorksGestational age is counted from your last period, about two weeks before conception, so a pregnancy of 6 weeks contains an embryo of about 4 weeks. Here is Naegele's rule derived, the correction for a cycle that is not 28 days, and when ACOG says an early scan should replace your dates.ExplainerWhat Is a Normal Menstrual Cycle Length? The Numbers, by Life StageFIGO puts a normal cycle at 24 to 38 days; ACOG's older range is 21 to 35. Here is why two respected bodies give different numbers, how much variation is normal, and how cycles change after menarche and before menopause.