McMillan Running Calculator

So if 19:00 is not a realistic goal for me at the 5K right now, what would have been a more appropriate goal? For that I turn to the McMillan Running Calculator, which uses your running time at a certain distance to estimate your times for other distances. I decided to use my best mile time, which I just recorded over the summer during track practices. We did the mile time as a performance indicator and I believe my best mile time was ~5:40 (I didn't write it down, I was ~5:50 the first time we did it this summer and I know my second time was faster). So, if I plug in 5:40 for my mile time into the calculator I get back a 5K time of … 19:38! Awww, that’s not good! I know I’m faster than that! Shoot… maybe my mile time was just slow… I thought I went all out but maybe I had a little more. What if I plug in 5:30, what’s my predicted 5K time then? 19:03! Hmmm, maybe I still have a little bit more to go before I can break 19 minutes at the 5K distance. Or maybe this calculator is wrong! :P