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Basal Body Temperature Chart

A basal body temperature (BBT) chart tracks your resting temperature each morning to detect the thermal shift that signals ovulation. After ovulation, progesterone causes a sustained rise of roughly 0.2-0.5 °F (0.1-0.3 °C) that lasts through the luteal phase. By charting your daily temps and calculating a coverline, you can confirm whether ovulation occurred and estimate when it happened.

Quick Answer

Your basal body temperature rises by about 0.2-0.5 °F after ovulation due to progesterone. A sustained rise above your coverline for 3 or more consecutive days confirms that ovulation has occurred.

These results are estimates based on general formulas and are not a substitute for professional medical advice. Consult a healthcare provider before making health decisions.

Temperature Unit

Daily Temperatures (°F)

DayDateTemp (°F)
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Enter your cycle start date and daily temperatures above, then tap Analyze to detect ovulation and view your BBT chart.

How the Formula Works

  1. Record your temperature at the same time each morning before getting out of bed.

    Measure BBT immediately upon waking, before any activity.

  2. Calculate the coverline from the 6 temperatures preceding the suspected shift.

    Coverline = Average of 6 pre-shift temps + 0.1 °F (or + 0.06 °C)

  3. Confirm the thermal shift when 3 consecutive temperatures meet or exceed the coverline.

    Thermal Shift = Temp(day N) >= Coverline AND Temp(day N+1) >= Coverline AND Temp(day N+2) >= Coverline

  4. Identify the ovulation day as the day immediately before the first elevated temperature.

    Ovulation Day = Day before first temp >= Coverline (in the confirmed shift)

  5. Estimate luteal phase length from ovulation day to the last charted day.

    Luteal Phase Length = Last Charted Day - Ovulation Day

Methodology & Sources

Reviewed and updated April 5, 2026 · Prepared by GetHealthyCalculators Editorial Team

This calculator uses the standard coverline method recommended by fertility awareness educators. The coverline is set at the average of the 6 pre-ovulation temperatures plus a small offset (0.1 °F). A thermal shift is confirmed when 3 consecutive readings meet or exceed this line, following guidelines consistent with the Sensiplan and Marquette methods of Natural Family Planning.

References

  • Fertility Awareness-Based Methods of Family Planning · American College of Obstetricians and Gynecologists (ACOG)
  • Basal body temperature recording in gynaecology and obstetrics · Fertility and Sterility
  • The Normal Menstrual Cycle and the Control of Ovulation · Endotext / NCBI Bookshelf
  • Standard Days and Basal Body Temperature Methods · World Health Organization (WHO)
  • Urinary hormone profiles during the natural menstrual cycle and the effects of age on hormone levels · Human Reproduction

Limitations

  • BBT charting can only confirm ovulation after it has occurred; it cannot predict ovulation in advance.
  • Illness, poor sleep, alcohol consumption, stress, and travel can cause temperature fluctuations that obscure the thermal shift.
  • Temperatures must be taken at the same time each morning before any activity for consistent results.
  • A monophasic chart does not necessarily mean anovulation — thermometer sensitivity and individual variation may mask a subtle shift.
  • BBT alone should not be used as a sole method of contraception without additional fertility awareness indicators.
  • This calculator provides an estimate and is not a substitute for clinical fertility assessment or ovulation predictor kits.

Frequently Asked Questions

What is a coverline in BBT charting?
A coverline is a horizontal reference line drawn on your BBT chart to help distinguish the lower pre-ovulation temperatures from the higher post-ovulation temperatures. It is typically calculated by averaging the 6 temperatures before the suspected thermal shift and adding 0.1 °F (0.06 °C). When 3 consecutive temperatures are at or above this line, ovulation is confirmed.
When should I take my basal body temperature?
Take your BBT first thing in the morning, at the same time each day, before getting out of bed, eating, drinking, or talking. Even sitting up can raise your body temperature slightly. Use a BBT-specific thermometer that reads to 0.01 °F (or 0.05 °C) for the most accurate readings.
How much does temperature rise after ovulation?
After ovulation, BBT typically rises by 0.2 to 0.5 °F (0.1 to 0.3 °C) due to the hormone progesterone. This rise is sustained throughout the luteal phase until your next period begins. Some women may see a sharp single-day rise, while others experience a more gradual increase over 2-3 days.
Can BBT charting tell me when I will ovulate?
No. BBT charting confirms ovulation retrospectively — you can see that it happened, but not predict the exact day in advance. Over several cycles of charting, you can identify patterns that suggest when ovulation is likely. For advance prediction, combine BBT with ovulation predictor kits (OPKs) or cervical mucus observations.
What does a monophasic BBT chart mean?
A monophasic chart shows relatively flat temperatures without a clear thermal shift. This may suggest an anovulatory cycle (a cycle where no egg was released), but it can also result from inconsistent temperature-taking times, illness, or a thermometer that lacks sufficient precision. If you consistently see monophasic charts, consult a healthcare provider.
How many cycles should I chart before relying on BBT data?
Most fertility educators recommend charting for at least 3 consecutive cycles to establish a reliable pattern. This allows you to account for natural cycle-to-cycle variation and gives you a clearer picture of your typical thermal shift timing and luteal phase length.
Can elevated BBT indicate pregnancy?
Yes. If your temperature remains elevated for 18 or more days past the confirmed thermal shift without a period, this is considered a possible early sign of pregnancy. However, a sustained rise alone is not definitive — confirm with a pregnancy test and consult your healthcare provider.

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