Pregnancy temperature chart: how to understand, track and interpret your chart

The pregnancy temperature chart is based on daily observation of the body's basal temperature. This corresponds to the temperature measured on waking, before any activity. This method of tracking is a recognised way to detect ovulation, identify your fertile window, understand hormonal fluctuations, and analyse menstrual cycles. When recorded accurately, it can also suggest a positive pregnancy temperature chart profile, particularly if the post-ovulatory rise is maintained for more than 16 to 18 days.

In summary

• A temperature chart remains elevated for more than 16 days after ovulation. This is a strong sign of pregnancy.
• Beyond 18 days without the return of your period, pregnancy is almost confirmed even before a urine test.
• A luteal phase typically lasts 12 to 14 days, with a thermal shift of 0.3 to 0.5 °C after ovulation.
• During IVF treatment, an Ovitrelle injection remains in the body for approximately 8 days. It can give false results on urine tests.
• This article is aimed at women trying to conceive, those using symptothermal methods, or those undergoing fertility treatment. It does not cover beta-hCG blood tests.

Updated on 5 May 2026

Basal temperature corresponds to the minimum body temperature, measured at complete rest. It varies primarily under the influence of progesterone. After ovulation, this hormone rises significantly, causing an increase in basal temperature. By plotting each measurement on a daily chart, a curve is obtained showing distinct phases: follicular (before ovulation), ovulatory, and luteal (after ovulation).

Temperature tracking is often combined with observation of cervical mucus. This is what is known as the sympto-thermal method. Studies show that the use of fertility indicators, including tracking cycle days, cervical mucus, cervical position, basal body temperature and urinary LH levels, is associated with an increase in fecundability.

Tracking your temperature helps you understand the structure of your cycle, anticipate ovulation, optimise your chances of conception, or identify irregularities such as an anovulatory cycle. For women hoping to conceive, the chart can provide an early indication even before a urine test comes back positive. A profile resembling a positive pregnancy temperature chart is characterised by unusual stability and thermal elevation during the luteal phase.

Choosing the right basal thermometer

A standard thermometer cannot be used — a specific thermometer is required, accurate to two decimal places, known as a "basal thermometer". This level of precision is essential to ensure the reliability of the method.

Digital or connected models are effective provided they have a memory function, which is useful if you forget to record a reading.

Ideal conditions for taking your temperature

Temperature should be taken every morning — not necessarily at exactly the same time — before getting up, after a minimum of three hours of uninterrupted sleep. The mouth, vagina or rectum all provide reliable readings, but the same method must be maintained throughout the cycle.

Keeping a journal or using a tracking app

Apps today make it possible to obtain automated charts, add symptoms (pain, cervical mucus, mood) and improve the accuracy of interpretations.

Follicular phase

It spans from the first day of your period until ovulation. Temperature is generally low during this phase, ranging between 36.1 °C and 36.7 °C depending on the individual.

Ovulation and temperature rise

Ovulation involves a slight drop in temperature followed by a sudden rise of 0.3 to 0.5 °C. This increase marks the rising secretion of progesterone.

Luteal phase and temperature maintenance

At the end of the luteal phase, as the corpus luteum regresses and serum progesterone levels decline, the basal body temperature returns to the lower range in the 1 to 2 days before menstrual bleeding begins, or just as it starts.

Temperature therefore remains elevated for approximately 12 to 14 days. If it stays high for more than 16 days, this is often referred to as a positive pregnancy temperature curve, but only a blood test can confirm pregnancy. You can also observe the cervical mucus after fertilisation, whose texture changes suddenly.

For a normal cycle

A normal cycle shows a low line in the follicular phase, a clear rise at the time of ovulation, and a high plateau during the luteal phase. If the plateau continues, this may potentially indicate that you are pregnant.

For a short cycle

A short cycle may show a brief follicular phase, sometimes fewer than 10 days. The thermal rise is the same but occurs earlier. The luteal phase remains essential: if it exceeds 14 days with sustained high temperatures, it may indicate a positive pregnancy temperature chart.

For a long cycle

Cycles that are longer in duration often feature an extended follicular phase, which delays ovulation. The chart may therefore remain low for longer. The interpretation remains the same: only thermal stability in the luteal phase gives indications of the possibility of being pregnant.

The temperature chart does not replace a positive pregnancy test, but it can indicate a probability. Sustained elevated temperature beyond 16 to 18 days after ovulation often corresponds to embryo implantation. However, factors such as stress, illness, or disturbed sleep can distort the curve. The method therefore remains an indicator, but never a certainty. If you are taking a pregnancy food supplement multivitamin type for your baby project, there is no reason for this to affect reliability.

Interpreting basal body temperature is not always straightforward. Even among experts in natural family planning, there is little consensus on the first day of the basal temperature rise between different observers. It has been reported that the timing of ovulation as determined by basal body temperature coincided with the LH peak ± 1 day in only 17 out of 77 cycles (22.1%).

For the chart to be reliable, regularity is essential: temperature taken upon waking, no movement, and the same conditions each day. It is important to note all factors that may affect readings: alcohol consumption, short nights, hormonal imbalance.

It is perfectly normal to notice some variations. Fluctuations of 0.05 to 0.1°C do not indicate anything abnormal. However, a sudden drop during the luteal phase may signal the onset of a period, whilst a prolonged plateau may indicate a possible future pregnancy.

A positive pregnancy temperature curve is characterised by a stable high plateau, with no drop before the expected date of a period. Some women even notice a slight secondary rise in temperature around 7 to 10 days after ovulation, sometimes corresponding to implantation. However, only a blood test can confirm pregnancy with certainty.

Kim · Cocooning · 5/5 · 01/06/2025

"This is my first cycle with Cocooning+ paired with Baby bump. The initial results speak for themselves. My post-ovulation temperature curve has stabilised, whereas before it was erratic (a slight hormonal imbalance). I also feel calmer and had no PMS."