What is the % reliability of temperature to determine sex


New Member
Apr 15, 2021
Location (City and/or State)

I was told by the breeder that it was 90% sure to be a female at the temperature he incubated the eggs, (Hermanns). is that about right? and what is the % accuracy for males at the lower temperature or is it about the same?

thank you


The Dog Trainer
10 Year Member!
Platinum Tortoise Club
Jan 9, 2010
Location (City and/or State)
Southern California
This is NOT reliable for any species except sulcatas. They are the only species that has been studied under lab conditions. We can all thank Mr. RIchard Fife for that study and this knowledge.

While it is generally acknowledged that warmer temps tend to make more females. These temps are not known for any species other than sulcatas, and few people have lab grade accurate incubators, even if we did know the exact temps. I intentionally let my incubators fluctuate a bit, because that is certainly what happens in the wild. Further, no one that I know of has held back a whole year's babies long enough to know the sex, and no one that I know of has paid for surgical sexing either. @zovick may have a good idea of the correct temps for radiata because of his extremely VAST knowledge and experience with that species (He was literally breeding them years before I was even born...) and he has also done and seen a good amount of surgical sexing. Most breeders sell off all their babies as soon as they can. I sure do. I get them started, put a little size on them, and then out the door ASAP! Babies are a tremendous amount of daily work and expense.

One example: I bought 14 baby platynota that were all "incubated for female". I raised them to maturity and ended up with 6.8. My ratio of males to females is better than anyone else that I know of. My buddy Gus bought 15 platynota hatchlings that were "incubated for female" and got 15 males.

This has been a source of annoyance for me for years now. I think some breeders truly just don't know better, while others do know better and they are just being dishonest to make a sale. People who are buying a baby sometimes want one sex or the other. The truth is that except for sulcatas incubated at the correct temps under lab conditions, the sexes of babies cannot be known without surgery. I tell my buyers what temperature I used during incubation of their baby and leave it at that. I make no guess about the sex. I know that I have produced both males and females of many species doing it the way I do it.