Note (October 2026): An earlier version said basal body temperature rises by one to one and a half degrees Fahrenheit after ovulation. According to Cleveland Clinic, the rise is usually about 0.4 to 1°F (0.22 to 0.56°C), and this has been corrected below.
Basal body temperature (BBT) is your body’s temperature at complete rest, measured right after waking. After ovulation, rising progesterone lifts BBT by about 0.4 to 1°F (0.22 to 0.56°C), according to Cleveland Clinic. Higher readings for at least three days in a row suggest ovulation has occurred, so charting BBT for several cycles reveals when you typically ovulate.
Key Takeaways
- Basal body temperature confirms ovulation after it happens; it does not warn you in advance.
- The post-ovulation rise is small, about 0.4 to 1°F (0.22 to 0.56°C), so a basal thermometer that reads to at least one-tenth of a degree is needed.
- Take the reading at the same time every morning, before getting out of bed, and chart it for at least three cycles to see a pattern.
- Alcohol, fever, poor sleep, stress, some medications, breastfeeding and time-zone travel can all skew readings.
- Used alone, BBT is not a reliable way to avoid pregnancy; the NHS says fertility awareness methods are 76% effective with typical use.
Today, we’ll talk a little bit about how to track ovulation through basal body temperature. Charting basal body temperature is one of the cheapest ways to see when you ovulate, although it confirms ovulation after it happens rather than predicting it in advance. There are also reasons for this.
- The first one is that it is very cheap and relatively easy to do as well. There are challenges while doing it but it also has benefits. Moreover, a sustained rise in temperature lets you confirm, after the fact, roughly when ovulation took place.
- It also provides you with a complete overview of your ovulation that can also help you in the future.
Your basal body temperature is basically the temperature at which your body is at complete rest. For instance, when you are in the bed and initially wake up, the temperature of your body at that moment would be your basal body temperature.
Progesterone levels rise after ovulation, and that hormone shift raises body temperature: according to Cleveland Clinic, BBT typically goes up by about 0.4 to 1 degree Fahrenheit, which is roughly 0.22 to 0.56 degrees in Celsius.
You can use this method by comparing your temperature when it continues to stay raised at a point versus the temperature that it was before yet.
Thus, it becomes a relatively easy method to track your ovulation period. It just uses a basal body thermometer which is easily available at your local drugstore or any Walmart nearby.
A standard fever thermometer is not precise enough. Cleveland Clinic recommends a thermometer that measures to at least one-tenth of a degree and says basal temperature on the packaging; it notes that a BBT thermometer costs about $10 at most drugstores. You can read more here about using these thermometers in the step-by-step section below.
Track your body temperature at the same time every day:
The first thing you need to do in the morning is to track your basal body temperature. It has to be checked at the same time each morning. An irregular work or sleep schedule makes readings less reliable; Cleveland Clinic gives the example of waking at 6 a.m. on weekdays but 8 a.m. on weekends.
Waking during the night, or moving around, talking or being awake for several minutes before measuring, can also change the reading. Moreover, if you are sick, then it will affect your body temperature for sure.
Alcohol, short sleep, stress, some medications, breastfeeding and travel across time zones can also throw off readings, according to Cleveland Clinic. It’s very easy when you are looking at your day to day temperature in your cycle chart.
Basal body temperature gives you a picture of the cycle in a very quick review, but it does not give you a lot of basic required information.
Your basal body temperature basically does not tell you before your ovulation. It tells you after it. Some women might have a decrease in their temperature before they ovulate but not everyone does.
It is very easy to confirm the ovulation after following the whole routine. Moreover, it’s really inexpensive as you don’t have to buy any kind of products each month. So, it helps in a positive manner in fertility monitoring.
How to Chart Basal Body Temperature Step by Step
The basal body temperature method works only when readings are taken the same way every day. Cleveland Clinic describes the routine as follows.
- Start on day 1 of your cycle. Begin on the first day of your period (the first day of bleeding) and continue every morning until your next period starts.
- Keep the thermometer by your bed. Take your temperature as soon as you wake up, before you stand up, talk or move around.
- Measure at the same time and from the same place. Most people measure by mouth; rectal readings also work, but do not switch between sites mid-cycle.
- Record every reading. Use a paper graph or a fertility-tracking app so each day can be compared with the last. The free period calculator and ovulation tracker can help you log cycle dates alongside your chart.
- Look for the shift. A chart shows two phases: lower temperatures before ovulation and higher ones after. When readings stay higher for at least three days in a row, you can assume ovulation has occurred.
- Repeat for at least three cycles. One chart shows what already happened; several charts reveal the day you usually ovulate, which is what makes the method useful for planning.
What Is a Normal Basal Body Temperature?
There is no single normal BBT; what matters is your own before-and-after pattern. Cleveland Clinic gives these typical ranges:
| Phase | Typical BBT (°F) | Typical BBT (°C) |
|---|---|---|
| Before ovulation | 96 to 98 | 35.5 to 36.6 |
| After ovulation | 97 to 99 | 36.1 to 37.2 |
| Size of the rise | About 0.4 to 1 | About 0.22 to 0.56 |
Some people see a slight dip just before ovulation, followed by a sharp rise. If pregnancy does not occur, BBT drops and the period usually starts a day or two later. If conception has occurred, BBT stays elevated because the body continues producing progesterone, but only a pregnancy test or a healthcare provider can confirm a pregnancy. Our guide to the best pregnancy tests covers that next step.
How to Use a BBT Chart When Trying to Conceive
The fertile window is the days when sex is most likely to lead to pregnancy. According to Cleveland Clinic, you are most likely to get pregnant from four days before ovulation to one day after it, because sperm can survive for up to four days, while an egg survives only about 12 to 24 hours after release.
Because BBT confirms ovulation only after it has happened, the chart is most useful for planning the next cycle. Cleveland Clinic’s example: if your temperature rose around days 12 to 16 in past cycles, having unprotected sex on days 8 through 16 of the next cycle covers the likely fertile window. Fertility depends on both partners, so the guide to ways to boost male fertility is also relevant.
BBT vs. Other Ways to Track Ovulation
Many providers recommend combining BBT with other fertility awareness signs, because each method has a different strength.
| Method | What it detects | Timing | Main limitation |
|---|---|---|---|
| Basal body temperature | Temperature rise caused by progesterone | Confirms ovulation after it happens | Easily skewed by sleep, alcohol, illness and travel |
| Ovulation (LH) test kits | Luteinizing hormone surge in urine | A positive result usually means ovulation within about 36 hours | Needs a new strip for each test |
| Cervical mucus | Mucus becoming clear and slippery, like egg whites | In the days just before ovulation | Takes practice to interpret |
| Calendar tracking | Cycle length over several months | Estimate only; most people ovulate about 14 days before their period | Unreliable with irregular cycles |
Sources for the table: Cleveland Clinic articles on basal body temperature and on ovulation.
Can Basal Body Temperature Be Used as Birth Control?
Basal body temperature on its own is not a dependable form of contraception. Cleveland Clinic says the method is not very effective at preventing pregnancy because so many factors affect temperature, and it is inaccurate with irregular cycles or missed readings.
The NHS groups temperature tracking within the fertility awareness method, which also records vaginal discharge and cycle dates. According to the NHS, fertility awareness methods are 91% to 99% effective when used correctly all the time, but only 76% effective if the instructions are not followed exactly, meaning 24 in 100 women would get pregnant in a year. The NHS advises learning the method from a trained fertility awareness practitioner, notes it can take 2 to 3 cycles to learn, and says it may not be suitable for people with irregular periods or those who must avoid pregnancy for health reasons. It also gives no protection against sexually transmitted infections.
When to Talk to a Doctor
A BBT chart can be a useful record to bring to an appointment. The NHS says more than 8 in 10 couples where the woman is under 40 conceive naturally within a year of regular unprotected sex, and advises seeing a GP after a year of trying. Women aged 36 and over, and anyone who already suspects a fertility problem, should seek advice sooner. Our article on conceiving after 40 covers age-related considerations. This article is general information, not medical advice.
Frequently Asked Questions
How much does basal body temperature rise after ovulation?
Basal body temperature usually rises by about 0.4 to 1°F (0.22 to 0.56°C) after ovulation, according to Cleveland Clinic. The size of the rise varies from person to person, which is why a sensitive basal thermometer is needed.
Can basal body temperature predict ovulation before it happens?
No. Basal body temperature rises only after ovulation, so a single cycle’s chart confirms ovulation rather than predicting it. Charting for several cycles shows the day you usually ovulate, which lets you anticipate it next time.
How many days of high temperature confirm ovulation?
Cleveland Clinic says that when temperatures stay higher for at least three days in a row, you can assume you have ovulated.
What can throw off basal body temperature readings?
Alcohol, fever from illness, not getting enough sleep, stress, some medications, breastfeeding and traveling across time zones can all affect BBT, as can measuring at a different time or after getting out of bed.
Does basal body temperature stay high if you are pregnant?
Yes, BBT typically stays elevated in early pregnancy instead of dropping before the expected period. A raised chart is only a clue, though; a pregnancy test or a healthcare provider confirms pregnancy.
Do I need a special thermometer for BBT?
Yes. A basal thermometer measures to at least one-tenth of a degree, and some show two decimal places, such as 98.15°F instead of 98.1°F. Cleveland Clinic notes these cost about $10 at most drugstores.
