Your primary goal should be to get active and stay motivated to keep moving.
Scott Douglas writing for the Washington Post:
If you’re the kind of exerciser who constantly checks your heart rate to ensure you’re in the fat-burning zone, you should stop. You’ll probably never meet your weight-loss goals that way. That’s because there’s no special fat-burning zone that’s key to getting lean.
Your body primarily fuels itself by burning a mix of stored fat and carbohydrates. The less active you are at a given moment, the greater the percentage of that fuel mix comes from fat. As your intensity of activity increases, the percentage of carbohydrates in that fuel mix also increases. At rest, fat constitutes as much as 85 percent of calories burned. That figure shifts to about 70 percent at an easy walking pace. If you transition to a moderate-effort run, the mix becomes about 50 percent fat and 50 percent carbohydrates, and it moves increasingly toward carbohydrates the faster you go.