How do you know if you don’t have any more belly fat, and then can work on your abs?

I’ve recently gotten into doing a lot of cardiovascular exercise in hopes of loosing that stubborn belly fat. I don’t have that much, and I’m hoping to tone up my midsection. I’m around 6’1 and weigh about 165-170. But, I’m curious to know, when do you know that its time to start working on your abs, and if some belly fat has burned off? Any tips would be awesome, thanks.