Understanding BBT curves

Each woman’s cycle is as different and unique as they are. However, it is helpful to have examples from which we can interpret your basal body temperature curve.

The "typical" curve

Typical curve

Here you see a "typical" temperature curve (28 days). Ovulation took place between day 12 and day 13, recognizable by the significant rise in basal body temperature. The corpus luteum phase (after ovulation) lasts 15 days and ends with the onset of menstruation.

Drop in the temperature curve before ovulation

Drop in temperature before ovulation

As you can see from this example curve, there are curves where the last value before ovulation (see arrow) is significantly lower than most other days measured before. The reason for this is the increased estrogen level shortly before ovulation. 

Good to know: This is the ideal day for sexual intercourse if you want to conceive.

Increased average value

Increased average value

A relatively high average temperature, as can be seen in the example curve, can indicate an over-functioning thyroid gland (Hyperthyroidism).

Other symptoms of hyperthyroidism may be:

  • long cycles
  • low menstrual bleeding 
  • general restlessness and nervousness
  • rapid, increased sweating

However, despite the increased average temperature, the basal body temperature curve shows the typical picture with an increase after ovulation and a significant increase during the corpus luteum phase.

Important: Whether you really suffer from hyperthyroidism can only be diagnosed by a doctor.

 Low average value

Low average value

A very low average temperature, as shown in the example curve, can indicate a possible under-function of the thyroid gland (Hypothyroidism).

Further indications of a hypothyroidism can be:

  • absence of menstruation or amenorrhoea
  • persistent heavy periods
  • irregular cycles
  • cycles without ovulation (no temperature increase)
  • short luteal phase
  • temperature fluctuations

However, despite the low average temperature, the basal body temperature curve shows the typical picture with characteristic increase after ovulation and significant increase during the corpus luteum phase.

Important: Whether you really suffer from an underfunction of the thyroid gland can only be diagnosed by a doctor.

Temperature outlier

Temperature outlier

If a measurement is clearly out of the range (see arrow in the example curve), Daysy will disregard it, but in case of doubt, Daysy will display as a yellow or red day.

Such one-time outliers can be caused by alcohol consumption, fever, too little or very long sleep, or by incorrect measurement. More about factors that influence your cycle .

Illness and fever

Illness and fever

A fever is when your body temperature reaches at least 38 degrees - if this is the case, you will most likely feel ill and you will notice that your temperature curve is unusually high (see example curve). Daysy will tolerate such strong outliers, but will display a yellow or red day in case of doubt

As a rule of thumb: If you wake up in the morning and feel differently than usual, for example sick, hungover or overtired, then skip measuring your temperature that day and each day until you feel better again.

Daysy is an intelligent fertility tracker that lets you get to know your very own menstrual cycle.