When runway length starts to look a little marginal, I do do those calculations, and on occasion it has informed by ability to carry pax or extra fuel.
Where I'm flying a C152 from a 1000m runway, no of-course I don't.
As a quick check I tend to use the GASCo quick reckoner, printed on A5 and kept at the back of my kneeboard. If it's more marginal than that, I get the manual out.
http://www.gasco.org.uk/upload/docs/...afety16-18.pdf for those who haven't met it.
G