# When will implantation happen?

Estimates when implantation happens: 6 to 12 days after ovulation, most often 8 to 10, from the last period and cycle length or the ovulation date.

- Page: https://www.acalculator.org/health/implantation-calculator
- JSON spec: https://www.acalculator.org/health/implantation-calculator.json
- Version: 4231ec713617

## Default answer

Example with the default inputs (What do you know? Last period, First day of your last period September 9, 2026, Cycle length (days) 28) on the example date Wednesday, September 30, 2026: Implantation most likely happens between October 1, 2026 and October 3, 2026.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| from | What do you know? | The first day of your last period, or the day you ovulated. |
| lmp | First day of your last period | The first day of bleeding of your most recent period. |
| cycle | Cycle length (days) | Days from the first day of one period to the first day of the next; 28 on average. |
| ovulation | Ovulation day | The day you ovulated, for example from an ovulation test or temperature chart. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| likely | Most likely implantation | The days implantation happens most often: 8 to 10 days after ovulation. |
| likelyFrom | Most likely from | The first of the most likely days: 8 days after ovulation. |
| likelyTo | Most likely to | The last of the most likely days: 10 days after ovulation. |
| from | Possible from | The earliest usual implantation day: 6 days after ovulation. |
| to | Possible up to | The latest usual implantation day: 12 days after ovulation. |
| ovulation | Ovulation | The ovulation day: entered, or the last period + cycle length − 14 days. |
| period | Next period due | The day the next period should start: 14 days after ovulation. |

## Method

Ovulation = last period + cycle length − 14 days (or the day entered); implantation 6 to 12 days after ovulation, most likely 8 to 10 days after.

## Assumptions

- Ovulation comes 14 days before the next period (ACOG average); real cycles vary.
- Implantation, seen as the first rise of hCG, happened 6 to 12 days after ovulation in pregnancies that lasted, and on day 8, 9 or 10 in 84% of them (Wilcox and others, 1999).
- These are estimates, not medical advice; spotting has many causes.

## Worked examples

1. from = period, lmp = 2026-09-01, cycle = 28 gives ovulation = 2026-09-15, likelyFrom = 2026-09-23, likelyTo = 2026-09-25, likely = September 23, 2026 to September 25, 2026, from = 2026-09-21, to = 2026-09-27, period = 2026-09-29. Source: ACOG (ovulation 14 days before the next period); Wilcox 1999 (implantation 6 to 12 days after ovulation, 84% on days 8 to 10).
2. from = period, lmp = 2026-10-01, cycle = 32 gives ovulation = 2026-10-19, likelyFrom = 2026-10-27, likelyTo = 2026-10-29, period = 2026-11-02. Source: Wilcox 1999.
3. from = ovulation, ovulation = 2026-12-28 gives from = 2027-01-03, likelyFrom = 2027-01-05, likelyTo = 2027-01-07, to = 2027-01-09. Source: Wilcox 1999 (6 to 12 days after ovulation, most often 8 to 10).

## FAQ

### When does implantation happen?

In a study that measured hormones in daily urine samples (Wilcox and others, 1999), implantation in pregnancies that lasted happened 6 to 12 days after ovulation, and on day 8, 9 or 10 in 84% of them.

### How is my ovulation day estimated?

Ovulation usually comes about 14 days before the next period. The calculator puts it at the first day of the last period + (cycle length − 14) days: 14 days after in a 28-day cycle, 18 days after in a 32-day cycle. If you track ovulation with tests or temperature, enter the ovulation day directly.

### What is implantation bleeding?

Some people notice light spotting around the days implantation is expected. Spotting has many causes, so this calculator cannot tell you whether spotting is implantation; ask a health care provider about any bleeding that worries you.

### When can I take a pregnancy test after implantation?

A home test detects hCG, which the body starts making at implantation. The level takes days to rise, so tests are most reliable from the day your period is due. See the pregnancy test calculator for the dates.

### Does late implantation matter?

In the same study, early pregnancy loss was more common when implantation came later: 13% for implantation by day 9, rising to 26% on day 10, 52% on day 11 and 82% after day 11.

### Can I use this after IVF?

Not directly. After an embryo transfer, the timing depends on the embryo’s age on transfer day. Ask your fertility clinic for the dates that fit your transfer.

## Sources

- Wilcox AJ, Baird DD, Weinberg CR. Time of implantation of the conceptus and loss of pregnancy. N Engl J Med. 1999;340(23):1796-1799. https://doi.org/10.1056/NEJM199906103402304
- American College of Obstetricians and Gynecologists. Committee Opinion No. 700: Methods for Estimating the Due Date (ovulation about 14 days before the next period). Obstet Gynecol. 2017;129(5):e150-e154. https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2017/05/methods-for-estimating-the-due-date