What is an implantation dip?

By the Safr team · Sources: peer reviewed research and clinical guidance cited below

Updated July 2, 2026

If you chart your basal body temperature, you may have watched your luteal phase temperatures sit high and steady, then noticed one lower reading around a week after ovulation. That single low day is what people online call an implantation dip. It is easy to read a lot into it. This page walks through what a dip actually is, what may cause it, when it tends to show up, and the honest limit: a dip can happen whether or not you are pregnant.

What causes a mid-luteal temperature dip?

The short version is that no one has proven a single cause. The most common explanation is hormonal. After ovulation, progesterone raises your resting temperature and keeps it up through the luteal phase. Around the middle of the luteal phase there is often a second, smaller rise in estrogen. Estrogen tends to lower body temperature, so the idea is that this brief estrogen surge nudges your temperature down for a day before progesterone keeps it elevated again.

Notice what that explanation leaves out. Estrogen rises in the mid-luteal phase whether or not an embryo implants, so the same mechanism can produce a dip in a cycle that does not lead to pregnancy. The name "implantation dip" suggests the dip is caused by implantation, but the timing is only a loose match, and the estrogen story does not require implantation at all. Everyday factors also move a single reading: a warmer room, a poor night of sleep, a later-than-usual measurement, or a glass of wine the evening before can each drop one day's temperature by a few tenths of a degree.

How big and how long is an implantation dip?

A dip is subtle and short. It is usually about 0.3 F below the surrounding luteal temperatures, and it lasts a single day. If your luteal readings sit around 97.9 F, a dip day might read about 97.6 F before returning to roughly 98.0 F the next morning. On a chart that looks like a small V. A drop that lasts two or three days, or one that keeps falling toward your baseline, is a different pattern and usually points toward your period arriving rather than a one-day dip.

Because the change is so small, measurement noise matters. This is why charting guides suggest taking your temperature at the same time each morning, before getting out of bed, after at least a few hours of sleep. Even then, one low reading is one data point. It is the shape of the whole cycle, not a single day, that is worth paying attention to.

When does an implantation dip happen by DPO?

Timing is where the name comes from. Implantation itself occurs 6 to 12 days past ovulation, most often 8 to 10 days past ovulation, according to a classic study of early pregnancy by Wilcox and colleagues. Reported dips cluster in a similar window, most often around 7 to 10 days past ovulation. That overlap is why the pattern got its name.

The overlap is also why the timing cannot prove anything. A dip at 8 days past ovulation lines up with the implantation window, but a mid-luteal estrogen dip lands in the same few days regardless of pregnancy. If you want to map your own days past ovulation and your estimated implantation window, our implantation calculator does the date math from your ovulation date. For the symptom side of that window, see DPO symptoms by day.

Does an implantation dip mean you are pregnant?

No. A dip raises the odds a little, but it happens in both kinds of cycles, so it neither confirms nor rules out pregnancy. This is the single most important point on the page, and the clearest way to see it is to compare two example charts. Use the toggle below to switch between a pregnancy cycle and a non-pregnancy cycle. Both show a one-day dip in the mid-luteal phase.

The dips look almost identical. What differs is the end of the cycle. In the pregnancy example the temperature stays elevated after the dip and keeps climbing, because progesterone remains high. In the non-pregnancy example the same one-day dip appears, but the temperature later falls toward the baseline as the period approaches. In other words, the dip itself is not the tell. What happens over the days after it carries far more information, and even that is not proof.

The numbers back this up. In Fertility Friend's published analysis of member charts, a one-day dip appeared in about 23% of pregnancy charts and about 11% of non-pregnancy charts. So a dip is roughly twice as common when someone turns out to be pregnant, but it still shows up in about one in nine non-pregnancy cycles, and most pregnancy charts show no dip at all. A pattern that is present in only a minority of pregnancy charts cannot be a requirement for pregnancy. For a fuller side by side, read BBT charts: pregnant vs not pregnant.

What about a triphasic chart?

A related pattern is the triphasic chart, where temperatures rise in three steps: the follicular baseline, the usual post-ovulation shift, and then a second sustained rise in the mid-luteal phase. The same Fertility Friend analysis reported that about 12% of pregnancy charts were triphasic. Like the dip, a triphasic rise is more common in pregnancy charts, but it appears in non-pregnancy cycles too and is missing from most pregnancy charts. It is a hint, not an answer.

Common questions

Keep reading

BBT charts: pregnant vs not pregnant · DPO symptoms by day · Implantation calculator · Am I pregnant? quiz