Hi Guys,

I'm not a mathematician but am seeking the help of someone with better 
maths skills than mine, so if anyone could help me I'd be very grateful.

I'm working on the design of a computer application at work, and one of 
the things we need it to do is reduce values by a fixed percentage over 
the year.  So, if we had a starting value of 10,000 and we wanted to 
reduce it by 12% we would end up with 8,800 at the end of the year.

However (and this is where I get stuck), the value needs adjusting each 
month by a fixed percentage to give us our final figure of 8,800 (and 
-12% total reduction).

I happen to know that the monthly percentage in this instance is 
-1.0596241% (trial & error got me that far).

But I need an equation or formula which will give me this figure.

I also need the formula to work if I need to reduce by any other 
percentage over the year.  For example, if I need to reduce my starting 
value by -20% over the year what fixed monthly percentage does this 
equate to.

If anyone could help I would greatly appreciate it.

Many thanks,

Jason