BBT Calculator: Basal Body Temperature Adjustment and Ovulation Indicator

Your details

Enter the temperature you read from your thermometer immediately after waking, before any activity.
degC
The hour you normally wake up (24-hour clock). Used to compute the wake-time adjustment.
h
min
The hour you actually woke up today. If you woke earlier than usual, the calculator adds a small correction; if later, it subtracts one.
h
min
Enter your six most recent pre-ovulation temperatures in cycle order to compute the FAM coverline.
degC
degC
degC
degC
degC
degC
Optional: enter three consecutive post-ovulation readings to check whether a confirmed thermal shift has occurred. All three must sit at or above the coverline and the third must clear it by 0.15 degC (0.3 degF).
degC
degC
degC
Adjusted temperatureThermal shift confirmed
36.5

Your measured temperature corrected for the time you woke up

Wake-time correction0
FAM coverline36.45
Reading vs coverline0.05
Thermal shiftThermal shift confirmed
0.05 above coverline
Pre-ovulation phase<-0.1At coverline-0.1-0.1Post-ovulation phase0.1+

Adjusted BBT: 36.50 degC

  • You woke at your usual time, so no wake-time correction was needed.
  • Your FAM coverline is 36.45 degC, based on the highest of your 6 pre-ovulation readings plus the standard 0.05 degC margin.
  • Today's temperature is right at or just above the coverline. Continue charting to look for three consecutive readings above it.
  • Three consecutive readings sit above the coverline and the third clears it by at least 0.15 degC: the FAM temperature rule is satisfied, confirming ovulation has occurred.

Next stepYour fertile window is now closed for this cycle. If you are trying to conceive and your period is late, take a home pregnancy test, as BBT staying elevated for 18 or more days after ovulation is a strong early indicator of pregnancy.

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