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One landscape page: your readings plotted to a fixed scale, the coverline where the "3 over 6" rule puts it, and every step of the working underneath.

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Basal body temperature chart

Read with the "3 over 6" rule · °C

Shift confirmed on cycle day 17Three readings in a row above the coverline, the third at least 0.2 °C higher.

Name Cycle starting Thermometer

°C 36.4 36.35 36.3 36.75 36.35 36.4 36.3 36.35 36.45 36.4 36.3 36.35 36.4 36.3 36.65 36.7 36.75 36.8 36.75 36.8 36.7 36.75 36.8 36.7 36.65 36.55 36.45 36.4

The working

Set aside before the rule ran: day 4.
Six lower readings, days 9, 10, 11, 12, 13, 14: 36.45, 36.4, 36.3, 36.35, 36.4, 36.3 °C. The highest is 36.45 °C, so that is the coverline.
Day 15: 36.65 °C, above the coverline. The first higher reading.
Day 16: 36.7 °C, above the coverline. The second.
Day 17: 36.75 °C. The third higher reading, and 36.75 ≥ 36.45 + 0.2 = 36.65. The rule is met.

What this chart can and cannot tell you

A temperature rise follows ovulation. It confirms in hindsight and never forecasts.
It cannot show a pregnancy. The NHS says most pregnancy tests can be carried out from the first day of a missed period.
No shift found is not proof of no ovulation: against hormone-confirmed ovulation across 193 cycles, a temperature shift was detected with a sensitivity of 0.23.
Not contraception, and not medical advice.

Rule as set out by Goeckenjan, Schiwek and Wimberger, Geburtshilfe und Frauenheilkunde, 2020 (PMC7360395).

Notes for this cycle

Athena — athenacycle.app Printed 4 November 2026

Choose Save as PDF as the destination to keep a file instead, and set margins to None.

This looks backwards. ACOG puts it plainly: basal body temperature "shows only when ovulation has already occurred, not when it is going to occur". A confirmed shift is a receipt, not a forecast, and the rule cannot say on which day ovulation happened.

This is not contraception. Fertility awareness has to be taught properly and combines several signs; followed imperfectly it is about 76% effective, meaning 24 women in 100 get pregnant in a year, and the NHS does not officially recommend any app or device for it. Nothing on this page is medical advice.

Change a reading or leave one out on the BBT coverline calculator, or print a blank grid for next cycle with the printable BBT chart.

Where this comes from

PubMed Central (2020). Continuous Body Temperature Monitoring to Improve the Diagnosis of Female Infertility. https://pmc.ncbi.nlm.nih.gov/articles/PMC7360395/
American College of Obstetricians and Gynecologists (2023). Fertility Awareness-Based Methods of Family Planning. https://www.acog.org/womens-health/faqs/fertility-awareness-based-methods-of-family-planning
PubMed Central (2022). Basal body temperature measurement and the ovulatory temperature shift. https://pmc.ncbi.nlm.nih.gov/articles/PMC9634753/
PubMed Central (2018). Continuous body temperature monitoring and the fertile window. https://pmc.ncbi.nlm.nih.gov/articles/PMC6265623/
PubMed Central (2021). Wrist skin temperature and basal body temperature compared against LH-confirmed ovulation. https://pmc.ncbi.nlm.nih.gov/articles/PMC8238491/
NHS (2022). Doing a pregnancy test. https://www.nhs.uk/pregnancy/trying-for-a-baby/doing-a-pregnancy-test/
NHS (2025). Irregular periods. https://www.nhs.uk/symptoms/irregular-periods/
NHS (2024). Natural family planning (fertility awareness). https://www.nhs.uk/contraception/methods-of-contraception/natural-family-planning/

Every link above was checked when this page was last updated. Athena is not affiliated with any of these organisations, and none of them has reviewed this page. Nothing here is medical advice.