If you fly out of an airport with a long runway, let's say 6,000 feet and you're flying your standard Cessna 172 (or similar), do you actually calculate your takeoff distance prior to takeoff or do you just up an go (after doing your pre-flight inspection and run-up obviously)? To follow up on that, if you do calculate it, and let's say based on your calculation you should have a takeoff roll of about 1,500 feet, would you simply use that as your abort point, basically saying if you're not in the air by 1,500 feet down the runway, you abort the takeoff since you still have 4,500 feet remaining? Do you add some sort of padding to the number (in case the wind has changed suddenly for example)? If you don't calculate it, what do you use as your abort point and what do you look out for to make that decision? The 50/70 rule on such a long runway really doesn't make any sense to me - I mean, if it takes you 3,000 feet to reach 70% of your Vr, something is majorly wrong, yet based on that rule, you'd still take off. This summer, I had an issue on takeoff and I'm wondering if I could have avoided being in that situation. I fly out of a long runway with a small two seater that is usually up in the air within about 1,000 feet. One hot and humid afternoon in August, I went flying at max T/O weight (which I rarely do, but that day I took someone who is on the heavier side). I did my run-up, all seemed normal. Lined up on the runway, advanced the throttle, rpm was right about at static max rpm, I rolled down the runway, feeling a little sluggish but airspeed came alive, Vr came along further down the runway than it normally would, but I chalked it off to being hot, humid and at max weight. Anyway, once in the air, I quickly noticed climb rate is really bad, I glanced at the rpm and it was about 300 below what it should be. I managed to still climb out to about 400 feet and hold altitude with the power I had and ended up landing on one of the airport's runways without an issue. Long story short, I had a stuck valve and couldn't make full power. How could I have avoided taking off in the first place? Now, every time I takeoff I obviously have this in mind and kind of also confirm my rpms are rising as I gain speed, basically doing: full power, confirm static rpm, confirm oil temp/pressure in green, confirm airspeed alive, confirm rpm raising, confirm Vr and rotate. What else can I do to ensure I make sound decisions while still on the ground?