Starting a BBT chart: A Simple Measurement Routine

A basal temperature chart is easier to interpret when the measurement routine is consistent. Before starting, decide what you want the chart to help with and whether it will fit your sleep and work schedule. More daily tasks are not automatically more useful fertility information.

Set up one measurement method

Choose a suitable digital thermometer and read its instructions. For a conventional oral BBT record, take the reading when you first wake, before getting out of bed or beginning your usual activities. Use the same method and aim for a similar time each day.

Keep the thermometer and a simple record nearby. You do not need an elaborate app to record a date, time and temperature. Our BBT overview explains what the pattern can suggest and what it cannot prove.

Preserve the actual reading

Write down the measured value and its unit. Note a missed reading as missing. If you change the thermometer or measurement method, record that change instead of treating the series as perfectly comparable.

Avoid filling gaps with the value you expected. A record with honest gaps is more useful than one that looks complete because uncertain information has been added.

Mark circumstances that may affect interpretation

Include a short note for illness, fever, markedly disrupted sleep, or a different waking time. Do not automatically adjust the number to make it resemble surrounding readings.

If your schedule changes frequently, the shift work guide may help you decide whether this routine is practical. A difficult schedule is a limitation of the method, not a personal shortcoming.

Decide when to review its usefulness

You can bring the chart to a clinician and ask whether it adds anything to your menstrual history. Temperature charts are not recommended as reliable clinical confirmation of ovulation, so do not postpone assessment while trying to produce an ideal graph.

If the routine is burdensome, discuss a simpler approach. The next useful step may be fewer measurements or a different assessment, rather than a more demanding version of the same chart.