As others have mentioned, without a HR monitor, the estimates are pretty pointless. They can vary SO much. I don't use myfitnesspal, but instead mammyride. Not because it's better, but because it's more exercise focused and keeps track of a lot of different stats. So here is an example as to how completely off those estimates can be. Yesterday I did a 3 hour ride. My average HR was 153, with substantial time above 170. On my iPhone app, it said I burnt 1600 calories. Likely an overestimate. But I was really pushing it, so it's actually probably not too far off. When I put it into mapmyride, it said 600 calories. That's not factoring in my HR, but rather just the distance I rode and how long it took. It doesn't consider that I climbed 3000 feet and much of the downhill was actually me popping the wheel up and over 1-2 foot roots (lots of effort). When you're connected to a HR monitor, that's indirectly considering that.

And also like others have said, everybody has a different calorie burn. All of these measurements are estimates. Some are more accurate than others, but none of them are actually correct. So many factors that you can't measure.

The best thing you can do is trial and error in terms of losing weight. And sadly, once you lose some weight, it's likely you'll have to trial and error again as your body will be changing.