So, let's say I have 10,000 and will expect an 8% yearly return on it. I figured out a formula or whatever that will give me the correct answer quickly:

10,000 * 1.08^n

Or say it was for 20 years: 10,000 * 1.08^20

This is great. But it doesn't do a whole lot because people generally contribute money regularly to their investments. Which gets me to my question...

I wanted to keep it simple. Let's say a person has $100. They invest it and can expect to earn 8% every year. Additionally, they add an additional $100 every year. The answer I got in Excel was $4,044.63 after 18 years.

After countless months beating my head against a wall and talking to my cat, I came up with this:

100(1+.08)18+100[((1+.08)18-1)/.08]

However, that equals $4,144.63. And to be honest, I don't remember how the heck I came up with that crazy looking equation. :(

But, it is giving me the wrong answer! By $100!!!!! I must be doing something right. lol

Can anyone help me simplify and understand this? Thanks!