Question regarding target Heart Rate

 Probably a noobish type question, but this just doesn't seem right to me.

Max Heart Rate is 220-Age(I'm 31) so my Max Heart Rate should be 189.

How the hell do I figure my Target Heart Rate for weight loss???  There seem to be a couple different calculations, I've seen 75% of my Max Heart Rate, but that only puts me at 142 which seems low.  Another calculation has me factoring in my resting rate.

A little help please.

Thanks in advance.

Max HR isn't determined by age. Using the Karvonen or Age Predicted Max Heart Rate won't accurately find your HR. Go talk to a trainer about doing a decent submaximal test, or get a medical standardized test for your actual MHR.