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Basal Body Temperature

BBT Charting Instructions

Basal Body Temperature measuring instructions are below. Please download a blank chart above.


The first day of menstruation is Day 1 of the cycle. Start a new chart on that day.
If menstruation starts during the day, transfer that morning’s temperature to a new chart.


Glass/mercury or digital thermometer

  1. If using a mercury thermometer, shake the mercury down below 35 degrees C the night before. If using a digital thermometer, try to find one with 2 decimal points.
  2. Take the temperature every morning immediately on waking, before getting out of bed or doing anything. If you have to get up at night, you should have had at least 1 hour of sleep or rest before taking your temperature. Note the recording time on the “Time” line at the top of the chart.
  3. Use the same temperature-taking route every day of the cycle: either (a) place the bulb of the thermometer under the tongue in contact with the floor of the mouth, close the lips and leave for five minutes, (b) insert the thermometer into the vagina for three minutes, (c) smear a trace of lubricating jelly on the bulb and insert into the rectum for three minutes. If you use a digital thermometer, please leave it in place for 3 minutes even if it beeps earlier (temp may continue to rise). Any change in temperature-taking route should be made at the beginning of the cycle. Note the temp-taking route under “Temp taken” on the right of the chart.
  4. Remove the Thermometer, read it and mark the result with a dot for each cycle day, either on the line or in the middle of the box. If you use a digital thermometer with 2 decimal points, round the temperature up or down as shown in the following example:
    • 36.50 = dot on 36.5 line
    • 36.51 = dot on 36.5 line
    • 36.52 = dot on 36.5 line
    • 36.53 = dot in the middle of the box between 36.5 and 36.6 to indicate 36.55 36.54 = dot in the middle of the box between 36.5 and 36.6 to indicate 36.55
  5. Clean the thermometer with a little cotton wool and cold water.

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Cycle no.

This shows how many cycles you have charted, i.e. start with cycle no. 1 for your first charted cycle, 2 for the second etc.

Cervical secretions

1  Secretions should be observed either at the vaginal opening/on toilet paper or by inserting one finger into the vagina and taking mucus directly from the cervix, but you should use the same method for the whole cycle. Secretions are observed by the feel, the look and the touch.

2  Describe the cervical secretions using shading in the appropriate box for “Mucus” (3 lines)

3  Mark each day of wet, slippery, transparent, stretchy secretions on line 1.

4  Mark each day of moist, white / cloudy sticky secretions on line 2.

5  Mark each day when no secretions are seen or felt (dry) on line 3.

6  Mark peak day by extending the shaded area in the column vertically upwards to correlate with the temperature readings

7  Mark each day of menstrual bleeding, including spotting under “Menstruation” (S=spotting, L= light flow, M=medium flow and H=heavy flow) Note: Peak day is the last day of highly fertile secretions and is marked on line 1. Peak day can only be recognised in retrospect (the day after peak) when the secretions have changed back to less fertile characteristics (in a box with a lower number – line 2 or 3).


The infertile cervix is represented by:

a solid black circle showing it to be closed
the circle is placed low down in the box, showing it lower in the vagina. an “f” under “Firmness” to indicate the cervix feels firm

The fertile cervix is represented by:

an open circle showing the cervix is more open.the circle is placed higher in the box, showing it higher in the vagina.

An “s” under “Firmness” to indicate the cervix feels soft

Cyclical symptoms

Indicate cyclical symptoms e.g. ‘mid-cycle’ pain, breast symptoms, mood changes etc. by appropriate day.


The temperature may be disturbed by:
– using a different thermometer
– errors or changes in the way the temperature is taken
– varying recording times
– change in environment (travel, holidays, change in climate or diet)
– stress, physical and emotional upsets
– drinking more alcohol than usual, partying late at night
– eating late in the evening
– lack of sleep or broken sleep, late nights, late mornings
– shift work
– illness, feeling unwell
– some drugs

If any of these factors apply, you should note them in the “Disturbances” line on the day on which they may have affected the temperature (e.g. if you party on cycle day 9, your temp may be higher in the morning of cycle day 10 so you make a note on cycle day 10).

Sexual intercourse

Mark with an X for unprotected or (X) for protected intercourse.

Over to you

I hope the above guide is helpful to you as an addition to your fertility journey. If you have any questions or comments, I would love to hear from you. Please contact me or leave a comment below.

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