Hi Kimberly! I use the calculator at soapcalc.net - hasn't failed me yet! I sometimes have slow tracing too, because I also hand stir. I use a lot of olive oil and also lard in my recipes, which are both slow to trace. If you're having trouble getting trace and the raw soap is cooling down, try heating it back up. Also, I find that if I stir for about 10 minutes, then leave it, then come back and stir again, and repeat that process a few times, I get trace faster.
You could also try hot process :) That's my new obsession. You don't have to worry as much about trace, and the soap is cured in a few days!