I'm writing a jQuery plugin for fast-counting up to a value when a page loads. Since javascript can't run as fast as I want it to for larger numbers, I want to increase the increment step so that it completes within a given timeframe, so I'd need a quadratic function that passes through origo and has it's turning point at y = target counting value and x = target duration, but I can't get a grip on the math for doing this. Since both the number and the duration can change, I need to be able to calculate it in javascript aswell.

Hopefully someone can help me with this one!