How women’s heart rate variability changes across the menstrual cycle
Your heart rate variability isn't flat across the month: it rises and falls naturally during phases of your cycle.
Heart rate variability is the variation in timing between heartbeats. Greater variability is generally considered better, whereas lower variability indicates strain on the body and sympathetic (fight-or-flight) activation.
HRV runs highest during your period, slides to its lowest in the weeks after ovulation, and climbs back when the next cycle starts.
In this guide, we explain how HRV changes phase by phase, backed by data from Ultrahuman users. We also examine how the Ultrahuman Ring reports HRV during cycle tracking.
- HRV runs highest during your period and lowest in the luteal phase, a swing of a few milliseconds that shows up consistently in the data.
- HRV and resting heart rate mirror each other across the month. When one rises, the other falls by a closely matching amount. They're two readings of the same underlying change.
- HRV is still above your baseline through the ovulation window. The drop comes after ovulation, not at it.
- Temperature is the signal the Ring uses to confirm ovulation. HRV tracks the phase, not the day.
- Women on hormonal contraception show a flatter monthly pattern.
How HRV changes in women
Figure 1
HRV and skin temperature across the cycle
Each night vs her own baseline · women · 4,881 members, 13,577 cycles
HRV and skin temperature across the cycle
Ultrahuman · overnight HRV and skin temperature by cycle phase
We looked at 13,577 cycles from 4,881 Ultrahuman members. Every night is scored against that woman's own baseline for that cycle, so the figures show how far each phase sits from her personal normal, not from anyone else's.
HRV runs highest during your period and slides to its lowest in the luteal phase, a swing of only a few milliseconds across the whole month. Skin temperature moves the other way, holding low and then stepping up after ovulation.
And there are key differences in HRV vs. men. In an analysis of 35,464 members across 165 countries, women recorded higher HRV than men from 9am to 3pm while running lower during sleep.
What the research says
A meta-analysis pooling 37 studies covering 1,004 naturally cycling women found HRV lower in the luteal phase than in the follicular phase. The difference was real but small enough that it came close to vanishing altogether.
A 2026 review of 16 wearable studies found that HRV ran roughly 3% to 9% higher in the early cycle than the late cycle.
For most women, that's a few milliseconds. But athletes, who start from higher HRV, can see a larger swing in their data.
The same review also found the change is flatter in women using hormonal contraception. If you're on the pill, expect a less pronounced monthly change in HRV.
How to see HRV in the Ultrahuman app
Your HRV appears each morning with your other overnight readings, and feeds your Dynamic Recovery Score.
Because HRV is one of the readings behind that score, a luteal night and a period night are not being compared like with like. Read the score the same way you read the HRV number itself: against nights from the same phase.
The Ring builds your baseline over your first few weeks of wear, then reads each night against it. Two habits make the number more useful.
Compare a night against nights from the same phase, rather than your best night of the month. And judge a change over a whole cycle rather than a week: a week isn't long enough to separate a phase from a trend.
Read the original research
All Studies →This explainer is based on original research by the Ultrahuman Science team. Read the source studies:
Frequently asked questions
Why is my HRV lower before my period?
Progesterone rises after ovulation and stays high through the luteal phase, which lifts resting heart rate and lowers HRV. In our data, HRV sits at its lowest point of the month in that stretch. It recovers once your period starts.
Should I compare my HRV to last week's?
Only if last week was in the same phase. A luteal night against a follicular night will show a difference that's mostly the phase, not a trend. Comparing the same phase across two cycles is the more honest read.
Does the pill change this?
Yes. Research on wearable studies found the monthly rhythm is flatter in women using hormonal contraception. You may still see night-to-night movement from sleep, alcohol and training, but the cycle-shaped pattern is weaker.
Can I use my HRV to know when I ovulated?
Not on its own. HRV is still above your baseline through the ovulation window and only drops afterward, so it reflects the phase rather than pinpointing the day. Skin temperature is the signal that does that job.
Is a low HRV in the luteal phase a problem?
Usually not. It's the expected shape of the month. What's worth attention is a clear change from your own usual pattern that persists across cycles, rather than a single low stretch where you'd expect one.
How many cycles before the pattern becomes clear?
Give it two or three. A single cycle can be knocked off shape by illness, travel, a hard training block or a disrupted night. You can't tell which until you have another cycle to compare it against.
References
- Schmalenberger KM et al. A systematic review and meta-analysis of within-person changes in cardiac vagal activity across the menstrual cycle. Journal of Clinical Medicine 2019. PMID 31726666
- de Jager S et al. Menstrual cycle effects on wearable-derived physiological measures: a living systematic review. Sports Medicine 2026. PMID 41545627
- Alzueta E et al. Tracking sleep, temperature, heart rate, and daily symptoms across the menstrual cycle. International Journal of Women's Health 2022. PMID 35422659
- Alzueta E et al. Menstrual cycle-related changes in sleep and cardiac measures in young and midlife women. Journal of Biological Rhythms 2024. PMID 39108015
This article describes associations in physiological data, not cause and effect. Population patterns describe groups rather than predicting any individual. If a reading or trend concerns you, speak to your physician.
