Technically, all exercise is fat-burning. You burn fat even while you sleep. But if you are training for appearance purposes, the question isn’t how much fat can you burn, but also how much fat you don’t store.
Think of it this way: if you gained one million dollars a year but you spent one million one, you’d be in a loss position. Same thing with fat balance: you might be able to burn an extra 2700 calories running a marathon, but if you eat an extra 3000 calories in a meal at McDonald’s (which is not that hard to do), you’d gain a bit of fat.
I weigh food to the very ounce and track all my calories eaten in a day. I can predictably lose fat even if I slept most of the day. It’s pretty simple to set up an effective diet; the hard part is sticking to it.
At the very least, your body will always try to compensate for the calories you burn by eating more food. So no matter how much fat you burn in a workout, if it stimulates your appetite to the point where your net fat balance is zero, then clearly you haven’t lost any additional fat.
Anyone who has dieted to lose weight knows how torturous it feels to have a constant urge to eat. Sorry to say, but this is how you know you’re losing fat. Nature doesn’t care that you have fat reserves; it needs it for a real famine, and wants you to eat if food is available. Going from overweight to “normal” (I hate that word) might not be as difficult as going from lean, to extra-lean.
Any fitness competitor or bodybuilder knows that during a contest diet their number one thought is, “when is my next meal?!”
Know this though: the effort that you put in is always rewarded. In other words, if you do everything right and are truly in a calorie deficit, you will lose fat. It’s like swimming and getting wet: you can’t have one without the other. In the case of human physiology, effort – big or small – is always rewarded.