Calculating recharge from a percentage?

I feel silly asking this considering how long I've played this game but... how can you calculate the recharge of a power by knowing the percentage of recharge reduction (Via enhancements, IO sets, hasten, etc)? That is... I know the base recharge of hasten is 450 seconds, I know I have... lets say, 110% (just to be a jerk and use an off number) recharge... how can I calculate what the recharge of hasten will be?

Thanks in advance!

Recharge = base recharge*1/(1+buff)

Buff of 110% is 1.1, which turns that into base recharge /2.1 = 450/2.1 = 214.3 secs

100% halves the recharge of a power
200% drops it to one third the base

There is a diminishing return built into recharge

Also, can't recall the simple way to show it, but there is a little bit of a trick for when the recharge changes part way through.

Thanks all!