Heh. So this is funny. I just tried out the test and it says I'm -3% off, meaning that it's actually UNDER-reporting my power.
I expected a different result altogether.
I weigh about 250 and figure on 30-40 calories per mile when I'm pushing myself, which for me means maintaining a speed of 20mph or better for as much as I can. Some people say that estimate is too high. When I used a stationary bike with a power meter and the same perceived effort I was burning about 35-40 calories per mile, but given on the road it's easy to get some free movement by freewheeling I usually estimate closer to 30 cal/mile unless it's very hilly.
So on that basis if I did 20 miles pushing hard all the way I'd figure I'd burned 600-800 calories (depending on hills, wind, and whether I was keeping my speed as high as I'd hoped). If you think you've burned 1100 calories so eat an extra 800 calories to compensate you think you're down 300 calories overall. If you really only burned 500 then you're actually gaining 300 calories. That alone means 2100 calories per week from that alone you'll gain a pound every 10 day or so.
If you're trying to lose weight, don't replace the calories...
Only additional food I eat is what is what I need to keep from bonking. I'm not trying to lose weight, yet.
We "compensatory" eat. In other words, we automatically eat more with the increase in activity.
One other "compensatory" effect, people reduce other activity when we work out. A study showed a nearly 1 for 1 decrease in activity, but the decrease came in small ways, such as sitting instead of standing and etc...
Overall there are not much hill, although I'm used to hills since I live on the side of a valley, but the route I ride climbs two very steep roads which are why it's so high. My knees are just fine, I have very strong joints lower, on account of olympic squats I think. My left hip is hinky, but that's from work and how odd I have to walk.
I've seen some calorie tracking app figures that suggest people are burning anything up to 90 calories per mile. Personally I think that sort of thing does far more harm than good because people come to expect that three 20 mile rides will burn off a pound of fat, and then wonder why the fat isn't coming off. Or they think they've burned off 1000 calories and eat an extra 500 calories to compensate when really they only burned 500 calories (or maybe even less). But there are some folks out there who will respond to any comments suggesting a more realistic calorie figure by saying they don't want the negativity or some such. The exercise is great but you need to be realistic about just how much work you've actually done.
It's also worth considering whether you're spending any of those 20 miles freewheeling. I remember my last 200km brevet and really struggling around the 160km mark. It was a really hot day, I hadn't drunk enough water and was struggling with the winds. Had there been a way to get back to the start without incurring silly costs in a taxi I'd have abandoned the ride, but my options were either pay a small fortune for a taxi or tough it out. So I stayed in a low gear and freewheeled as much as possible. Out of the last 40km I covered several of them with minimal energy expenditure - it takes very little effort to freewheel down a hill doing nothing more than keeping the bike upright. Based on my normal estimates, did I burn 125 miles x 40 cal/mile = 5000 calories? Highly doubtful, I tend to pace myself on a brevet and the last 25 miles were in full-blown energy conservation mode so I'd figure more like 100 miles x 20 cal/mile = 2000 calories. And that's based on weighing 25% more than you do.
There's such a wide range of calorie figures out there and it's hard to take them seriously when they vary so widely. The way to find out for sure is to use a power meter but short of that I'd rather estimate low than estimate high. The only time I'd look to estimate high is if I was working hard enough that taking on sufficient food was a matter of avoiding bonking and being stranded in the middle of nowhere, rather than being hungry when I got to the end.
To the OP, to truly burn 50-60 calories per mile like the calculators suggest, you'd probably need to add a backpack with at least 50 lbs of weight in it on each ride. I have a friend who started doing that after he lost about 75 lbs riding and wanted to get his burn back to where it was when he started. He says it's miserable at first, but works wonders if you stick with it. So it can be done.
In the end, just keep riding hard and monitoring your diet carefully. You'll get there.
And if you're the type of person where the data and numbers get to a point where they are stressing you out, detracting from the enjoyment of the ride, and decreasing the drive to push yourself, try this:
The big question is what is the terrain? If you're doing smaller rollers where you carrying momentum from one downhill to the next uphill you will burn many fewer calories that extending climbing and descending.
Today I weighted in at 187. I am suspecting that my weight is from water and not from eating, because 1400 calories/day is 400 LESS than what I need to be eating to lose 2 pounds per week, so it did not make any sense. I was extremely alarmed, however, because that nearly 5 pounds of weight increase represented over two weeks of work.
Today I went on a 50 mile ride, meant to go on 40, but I hit 40 and said, "I could do another 10." I noticed that right around 40 I hit this wall, I began to feel very drained, as if I had no energy left, which makes sense because I doubt my body can do much in the way of storage on a 1400 calorie diet. Well, I popped two servings of fig newton and it got much better, although I was still feeling it. Good to know for longer rides, though, I'll make sure to begin eating sooner than the 40 mile mark.