Does HRV change across the menstrual cycle? Reading a lower value before your period

What is HRV in the first place?

Heart rate describes how many times the heart beats in a minute. Heart rate variability, or HRV, describes how much the interval between successive beats changes. The heart does not always beat at identical intervals like a metronome.

Apple Health calculates this variation using SDNN, usually recorded in milliseconds. HRV is related to autonomic regulation of the heart, but does not directly measure the autonomic nervous system.

Age, breathing, posture and time of measurement can affect HRV, as can sleep, exercise, alcohol, health and medication. There is therefore no single number that is normal for everyone.

What are the first and second parts of a cycle?

The first day of menstrual bleeding is cycle day 1. The follicular phase runs from the start of menstruation to ovulation; the luteal phase runs from ovulation to the next period. “Premenstrual” generally refers to the later luteal phase.

Ovulation timing differs between people and from one cycle to another. Day 14 is not always ovulation day. Recording period start dates alone does not establish whether or when ovulation occurred.

• Follicular phase: from the start of menstruation to ovulation
• Ovulatory phase: when an egg is released; the exact day cannot be known from a calendar alone
• Luteal phase: after ovulation until the next period
• Premenstrual phase: generally the later luteal phase, with duration varying between people

Research tends to find lower HRV later in the cycle

A 2019 analysis combined 37 studies involving 1,004 people. HRV measures such as RMSSD and HF were, on average, lower after ovulation than before it.

The analysis used a measure called d to compare effect sizes across studies. The result was d = −0.39; the minus sign indicates a lower value after ovulation. It does not mean HRV fell by 39%.

The 95% confidence interval, describing uncertainty around the estimate, was −0.67 to −0.11.

When cycle phases were divided more finely, statistically significant decreases were found in five studies with 200 people comparing menstruation with the premenstrual phase, and eight studies with 280 people comparing the mid-to-late follicular phase with the premenstrual phase.

However, the numbers of studies were limited and their findings varied considerably. The average cannot directly predict an individual’s pattern. Other phase comparisons did not show clear differences. We cannot say HRV stays equally low throughout the post-ovulation period.

A 2026 review covered 16 wearable-device studies. Fifteen of these studied people with natural menstrual cycles, involving 15,273 participants. HRV tended to be higher early in the cycle and lower towards its end. Individual studies reported differences of about 3–9% for HRV calculated from beat intervals.

Neither review showed that everyone’s HRV must fall before menstruation. Devices, calculations, measurement periods and phase definitions differed. In the 2026 review, methodological differences were too large to combine every result into a single pooled estimate.

Individual differences matter

In another 2026 study, 21 people with natural cycles measured HRV daily. Urine tests for the pre-ovulation rise in luteinising hormone (LH) were used to estimate ovulation and align cycles around that date.

There was no pattern shared by everyone, but there were patterns that differed by individual. Lower RMSSD was also associated with poorer sleep quality and greater stress or fatigue. This did not establish cause and effect.

These findings do not invalidate the earlier research. Different participants, measurements and ways of aligning cycles can produce different results. The current picture is that group averages show tendencies while individual patterns are more complex.

Different calculations can share the name HRV

There are several HRV calculations. Their names may sound similar, but they reflect slightly different features.

• SDNN: variation across all beat intervals in the measurement period
• RMSSD: differences between neighbouring beat intervals
• HF: beat-interval fluctuations at frequencies close to breathing

Five checks when HRV looks low before your period

1. Check when and how it was measured

   Was the record made during sleep, after waking or during a mindfulness session? Check whether there are unusually few records that day.

2. Compare with your recent history, not other people

   Review your own weeks of data on the same Apple Watch rather than age-group averages or social media numbers. Avoid concluding anything from one rise or fall.

3. Add cycle dates

   Record the first day of menstruation and note how many days before the next period, or which day of bleeding, a reading occurred. An app’s predicted ovulation day is not confirmed ovulation.

4. Look at sleep and personal experience too

   Consider sleep duration, awakenings, resting heart rate, pain, fatigue, mood, alcohol and intense exercise together. HRV alone cannot identify the cause.

5. Review several cycles

   If possible, look across two or three cycles or more to see whether similar changes recur at similar phases or differ each time. This is a practical review guideline, not a research-established required duration. Even a repeating pattern does not prove the menstrual cycle caused it.

In Feelmo, treat the cycle as context

In Feelmo, begin with your own experience: sleepy, in pain, tired or low in mood. Adding period records, sleep, heart rate and HRV can make recurring personal patterns easier to review.

Feelmo Balance is a proprietary guide for reflecting on day-to-day condition. It is not a test of hormone levels, ovulation, PMS or autonomic nervous system function. Cycle dates, HRV and feelings changing together do not establish a cause or a treatment effect.

Contraception, pregnancy and menopause need separate consideration

The main studies discussed here involved people with natural cycles who were not using hormonal medication. Their results cannot simply be applied to people using hormonal contraception, those who are pregnant, postpartum or breastfeeding, or those going through menopause.

The 2026 review also included research on hormonal contraception and after menopause, but study numbers and classifications remain limited. With irregular cycles, do not identify follicular and luteal phases from dates alone. Use your records to support discussion with a clinician.

What HRV alone cannot determine

If premenstrual mental or physical difficulties recur each month and affect work, school or daily tasks, consult a gynaecologist or another healthcare professional regardless of HRV. Recording symptoms and period dates for two or three months can help describe the pattern. For sudden severe pain, heavy bleeding or fainting, seek medical care without waiting to complete records.

• Whether or when ovulation occurred
• Whether you have PMS, PMDD, pregnancy or a gynaecological condition
• Whether your autonomic nervous system is “out of balance”
• Whether you should exercise or rest that day
• The cause of pain, bleeding or mood changes