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What is the basal temperature before my period?
Last reviewed: 08.07.2025

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Basal temperature before menstruation can give answers to a woman's condition and her hormonal activity. Therefore, in order to plan her life, every smart woman should understand the phases of her cycle and be able to control all processes.
Cycle regulation in women and basal temperature
It can be helpful for any woman to create a menstrual calendar or a special chart of her cycle. By doing so, you can get to know your body, know what is normal for you, and have benefits for your own health. Your menstrual cycle can basically be divided into phases: the preovulatory infertile phase, the fertile phase, and the postovulatory infertile phase. You can determine which stage you are in by monitoring the three main fertility indicators: basal body temperature, cervical fluid, and the position of the cervix.
The menstrual cycle is directly influenced by estrogen and progesterone, and the body reports the status of these hormones daily. Estrogen dominates the first part of the cycle; progesterone dominates the latter. Another hormone, called luteinizing hormone (LH), is a catalyst that stimulates the ovary to release an egg. Ovulation (the release of an egg) occurs once per cycle. During ovulation, one or more eggs are released. The egg can be active for 12-24 hours. All of these processes affect the basal body temperature.
Women who have natural menstrual cycles have a biphasic basal body temperature pattern. The first phase of your cycle has low temperatures, and the second phase of your cycle has higher temperatures.
The first phase is called the follicular phase. This phase begins on the first day of your period each cycle and ends at ovulation. After ovulation is the luteal phase. After ovulation, the corpus luteum (the remains of the follicle that released the egg at ovulation) produces the heat-inducing hormone progesterone. The progesterone produced by the zona lutea during your luteal phase raises your core body temperature. The primary reproductive function of progesterone in the luteal phase is to cause changes that prepare the lining of the uterus for implantation of the fertilized egg. However, progesterone also causes your resting body temperature to rise after ovulation. Because progesterone is only secreted at high levels after ovulation, it is possible to detect ovulation during the day before your temperatures rise when the temperatures are plotted on a chart. The temperature range can vary from woman to woman, as each person is unique. If you are not pregnant, your temperature will remain elevated for 10 to 16 days until the corpus luteum regresses. At this time, if you are not pregnant, your progesterone levels drop sharply and you get your period. Your temperature usually drops at this time as well, although it is not uncommon to have fluctuating or high temperatures during your period.
But keep in mind that basal body temperature is your body temperature at rest, unaltered by other factors. It can be used to reliably confirm ovulation because progesterone, which is only produced during the luteal phase, increases your core body temperature.
Characteristics of basal temperature
Taking your body temperature regularly can help you know when you're ovulating. There's usually a drop in temperature just before ovulation and a sudden rise afterward.
What is basal body temperature? This is the lowest reading of your body temperature when it is taken in the morning after rest. This is the baseline reading that is then used to compare any increases or decreases throughout the month. For the readings to be effective, a woman needs to take her temperature before she even gets out of bed and if she has slept for at least four hours, preferably more. It is very important to take her temperature before eating, drinking, going to the bathroom, and before any sexual activity – all of which raise your heart rate and, in turn, your body temperature from your baseline.
How to measure? A digital thermometer can be easier to use than a mercury thermometer, and it is important to have a thermometer that measures Celsius rather than Fahrenheit. Specially designed basal body temperature thermometers are available at drug stores. In terms of accuracy (which is important when measuring basal body temperature), it is worth buying a new thermometer. Basal thermometers give more accurate temperature readings than standard digital thermometers. When using a basal thermometer, it is important to follow the manufacturer's instructions. Each design is slightly different, and it is important to follow the steps for proper use to ensure accuracy.
The thermometer should be placed under the tongue and left there until it beeps. If you are using a mercury thermometer, it must be left there for three minutes to get an accurate reading.
When to start measuring your basal body temperature? On the first morning of your menstrual cycle, as this marks the beginning of each cycle. It is important to be sure that the reading is accurate.
How do you properly plot your basal body temperature? Take your temperature reading and mark an X in the box where the date and temperature intersect. Connect each dot with a line and see if there is a change throughout the month, with the line going up or down. Over time, you will likely see a pattern of degrees that reflects your ovulation patterns.
For each new month and each menstrual cycle, it is important to start a new chart. For each day of the month that you had intercourse, circle the corresponding day or place a small symbol that looks like an asterisk (*) in the box at the bottom of the chart.
Remember that it is not so much the individual temperature measurement that is important, but the pattern of change between the first and second half of the cycle. Typically, there is a lower temperature reading in the first half (before ovulation) and a higher "spike" (after ovulation) in the second half.
How does your basal body temperature change throughout the month? During a regular 28-day menstrual cycle, your normal body temperature is around 98.5°F (36.5°C). Just before you ovulate, your temperature will likely drop to 98.2°F (36.2°C). It is normal for this to happen during days 13-14 of your cycle. Then, just as you ovulate, your temperature will increase, and will continue to rise until it reaches 99.5°F (37°C), where it will remain until your period.
What should the basal temperature be before menstruation? The norm for this value is individual. But on average, this figure reaches 37, and then gradually decreases. How many days before menstruation does the basal temperature decrease? As a rule, 3-4 days before menstruation there may be a slight decrease in temperature, but not lower than 36.8. The basal temperature the day before menstruation drops a little more to 36.5, and then just before ovulation it reaches its lowest figures. Thus, the basal temperature graph before menstruation has a constant value and is slightly lower than after ovulation. The basal temperature before menstruation may differ during the day and in the evening, but these values are not significant.
But the basal temperature can be 36, 37, 38 before menstruation, which can be an individual feature or can reflect the presence of a concomitant condition in a woman.
Therefore, women typically need to track their basal body temperature for three or more months before they see a predictable pattern. It takes time to build confidence in being able to predict ovulation or menstruation through temperature changes and other body changes.
Factors that may disrupt morning temperature include fever, alcohol consumption overnight, less than three consecutive hours of sleep before taking temperature, and thyroid status.
How accurate are these basal body temperature changes? Keeping a basal body temperature is not an accurate predictor of ovulation. In many ways, it is more useful as a tool to measure ovulation after it has occurred rather than before. Keeping a record and then interpreting the pattern of temperature rises and falls will help you know when your most fertile time is likely to be. But remember, this is not a guarantee that you will get pregnant, and there are several factors that need to be in alignment before conception. Not all women experience a rise in their temperature when they ovulate, and while this is considered normal, it is not a consistent pattern among all women.
There may be several reasons for the rise and fall of basal body temperature before menstruation. What is an extremely low basal body temperature? There is usually a small difference between the low temperature phase and the high temperature phase: this difference is from 0.3 to 0.5 ℃, and the basal temperature level is usually in the range of 36 to 37 ℃.
If you have less than 36.5℃ even during the high temperature phase, it means you have a low basal body temperature.
Low basal body temperature can be caused by many reasons, but one of the reasons is related to changes in hormone levels. Since female hormones affect temperature, changes in the levels of secreted hormones, in addition to stress, accumulated fatigue or lack of sleep, changes in diet can cause the body temperature to remain low. In addition, an unhealthy diet that does not keep the body warm enough or having foods that can lower your BBT levels and thus impair blood circulation is a factor that can contribute to a low basal body temperature. Even if you have adapted well to the problems and continue to maintain a healthy lifestyle, increased levels of hormone secretion can cause your thyroid or your reproductive organs to function more slowly and contribute to a low basal body temperature. It is recommended that you visit a doctor and get yourself checked if you have a consistently low basal body temperature for a period of 3 to 4 weeks.
A low basal body temperature can be corrected to some extent by making lifestyle changes. Having a regular schedule that you follow, getting enough sleep, and eating a balanced diet can help regulate hormone secretion and increase your temperature. Find ways to help yourself manage stress and don’t let it build up, as stress can affect hormonal secretions.
An increase in basal temperature may be due to illness and systemic hyperthermia, so this fact must be taken into account with such changes.
Basal temperature before menstruation may change, which gives you the opportunity to plan your affairs with an irregular cycle. But you can only evaluate basal temperature after a thorough analysis of temperature charts, which are built based on your observations for at least three months in a row.