I candle after about 6 or 7 days and usually can tell by that time whether i have a good egg or not, but i do not toss any eggs until after day 10. By then you should be able to tell with little or no doubt whether you have good eggs. After day 7 i candle about every other day sometimes i go 2 or 3 days without doing it. The main reason i candle is to get rid of the bad eggs so that i don't end up with a mess in the bator, and it is kinda cool to see the little guys moving inside the egg. I use a large mag-lite and it works great.