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Basal Body Thermometer Guide

How do I know which basal body thermometer is right for me?

The benefits of basal body temperature (BBT) charting are well-known among the community of women who are trying-to-conceive. A carefully kept BBT chart provides valuable information about your menstrual cycle, and can help you pinpoint your fertile window. By timing your lovemaking on the days that you are most fertile, you will increase your chances of conception.

Basal body temperature is the lowest temperature attained by the body during times of rest (usually after sleeping for several hours). One of the key physiological changes that occurs at the time of ovulation is an increase in basal body temperature, which results from an increase in progesterone levels, the hormone that warms the body in preparation for pregnancy. By taking your BBT each morning throughout your cycle and charting the temperatures, you will be able to detect the rise in BBT that follows ovulation. This thermal shift typically occurs about 24 hours following ovulation, so it doesn’t help you predict ovulation for current cycle. However, charting your temperatures in your current cycle can help you predict ovulation for subsequent cycles. For some women, the temperature shift that occurs at ovulation is less than one-half degree. As a result, successful BBT charting requires the use of an accurate and sensitive thermometer that can detect very subtle changes in your resting, or basal, body temperature.

At, we offer two types of basal thermometers: mercury-free glass and digital. A common question we receive is “Which type of basal thermometer is better?” Our answer: “It depends!”  When choosing between the two, we recommend considering the following factors: accuracy, affordability, and convenience and ease of use.  No matter which basal thermometer you choose to purchase from, you can rest assured that you are purchasing and accurate tool for BBT tracking. And, both types come with ovulation charts to make BBT charting quick and easy.



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Accuracy: There are two types of accuracy that pertain to basal thermometers: absolute accuracy and relative accuracy. Absolute accuracy refers to the ability of the thermometer to correctly measure your actual temperature. Relative accuracy refers to the ability of the thermometer to provide readings that are accurate in relation to other readings provided by the thermometer. While both types of accuracy are helpful, relative accuracy is of particular importance in basal body temperature charting. While both the glass and digital basal thermometers are highly accurate and perform comparably in regard to relative accuracy, in general, glass thermometers tend to provide greater absolute accuracy than their digital counterparts. Our digital thermometer provides readings to 1/100th of a degree (97.83, for example), which allows for accurate charting to 1/10th of a degree (97.8, for example).

Affordability: Although glass thermometers are typically more expensive than digital thermometers, both types are relatively inexpensive and will last for a long time. At, our digital basal thermometer sells for $8.95.  You may also find a digital basal thermometer at your local drugstore, where you will likely pay between $11 and $15 for a thermometer with similar features as the one sold at Early-Pregnancy Glass digital basal thermometers are more difficult to find in retail stores. Our unique mercury-free basal body thermometer sells for $21.95, and is a safe and environmentally-friendly alternative to traditional mercury thermometers.

Convenience and ease of use: The method for taking your BBT is the same whether you are using the glass thermometer or the digital thermometer. Immediately upon waking in the morning, before you even get out of bed, you place the thermometer under your tongue. A digital thermometer will read your temperature in about one minute, while it may take up to three minutes to attain a reading with the glass thermometer. Once you have an accurate reading, you will plot the temperature for the day on your BBT chart. Some customers find it difficult to read the glass thermometers (at, our glass thermometer comes with a special magnifying case to help make reading the thermometer easier). As a result, many women find the digital basal thermometer, with its large, easy to read digital display, to be more convenient and user-friendly. In addition, our digital basal thermometer includes a beeper to indicate when it is done taking your temperature reading and memory recall of your last reading. Some commercially available digital thermometers also have the ability to read temperatures in both Fahrenheit and Celsius, and are backlit for easier reading in the dark.