Below is a summary of the rules for Trying To Avoid (TTA) from the book Taking Charge of Your Fertility (TCOYF) (20th Edn). It is considered by many as the “FAM Bible.” The majority of members in our community that have self-taught did so through this book.
Amazon US https://amzn.to/30VvI8f or Amazon UK tinyurl.com/y5xau68a
(all rules pertain to temps in Fahrenheit, not Celsius)
RULE 1 – FIRST 5 DAYS RULE
You are safe the first five days of the menstrual cycle if you had an obvious thermal shift about 12 to 16 days before.
RULE 2 – DRY DAY RULE
Before ovulation, you are safe the evening of every dry day. But the next day is considered potentially fertile if there is residual semen that could be masking your cervical fluid.
RULE 3 – PEAK DAY RULE
You are safe the evening of the 3rd consecutive day after your Peak Day, the last day of egg white or lubricative vaginal sensation
RULE 4 – THERMAL SHIFT RULE (STANDARD SHIFT)
You are safe the evening of the 3rd consecutive high temp past your Peak Day, as long as that 3rd temp is at least 3/10ths above the coverline.
> Example charts shown here
WEAK THERMAL SHIFT
You are safe the evening of the 3rd consecutive day your temperature is above the CL, as long as the 3rd temp is at least 3/10ths above. However, if it doesn’t reach a full 3/10ths, you could still rely on FAM for contraceptive purposes by waiting until the evening of the 4th temp above the coverline.
> Example charts shown here
FALL-BACK RISE
A fallback rise occurs when there is a temperature drop on Day 2 of the temperature shift, followed by a sustained temperature rise. If it is only a one day drop, there is no need to re-draw the coverline. If you are TTA, to be conservative, start the count over again after the second sustained rise to be absolutely sure that the egg(s) are dead and gone. If you don’t wish to do this, you could, instead, rely on the Peak Day rule to signal the start of the infertile phase (if you do this, you may wish to ensure that you are dry, that your temps are above the CL, and your cervix has returned to its infertile state of low, closed and firm).
> Example charts shown here
SLOW RISE SHIFT
Instead of your temperature shifting by at least 0.2F higher than the highest of the previous six, you may see a rise of only 0.1F at a time. This is slow rise > if you notice that your temp rises 0.1F higher than the highest of the previous six, and then rises another 0.1F the next day, draw the coverline through the previous days’ temperature. Once your temps remain above this coverline for three days, and the third temp is at least 0.3F above the coverline, then you can consider yourself safe from the evening of that third night.
If that third temp is not 0.3F above the coverline then take extra precaution and stay protected until either:
1. The evening of the 4th temp above the coverline, or
2. The evening of P+4 (rather than P+3)
> Example charts shown here