ARGH! Need maths help!

[blamebrampton]

I was once good at maths.

I know I should know how to do this, but I cannot remember enough to see if my method is effective or not. I found a website that will let me punch in numbers and give me an answer, but I want to check it! So I am hoping that shocolate  or someone similarly gifted is up and about.

I start with $50. Every week, I add $50. I have a compounding interest rate of 9.96%. I compound it annually, or monthly (two results). What do I have at the end of 21 years?

More than happy to do all the actual working if someone can remind me of what the formulae are.

Comments

[sherryillk.livejournal.com]

Try this: http://www.mathhelpforum.com/math-help/business-math/60410-i-have-question-annuity-calculation.html

It seems to be along the lines you are looking for... But it seems to yield a pretty bad-ass looking equation that makes me want to run for the hills... >

[blamebrampton.livejournal.com]

Cheers dear! Alas, it does not work for me when m>c :-(

[sherryillk.livejournal.com]

But the equation states that it will work when m > c, m < c and m = c, just not when it's compounded continuously...

Anyway, I went and tried both scenarios and I got $196,083.16 when it's compounded once annually and $184,053.28 when it's compounded monthly. I tried to be as accurate as I can but it's hard when the only calculator you have is your computer one... >< It really made me wish I had my graphing calculator but alas, it's been lent out to my brother...

[blamebrampton.livejournal.com]

I've lost track among all the calculations tonight, but that sounds familiar, except monthly must be > than annually, so it can't be right :-(

It's too late, I am off to write fic!

[sherryillk.livejournal.com]

Whoops, went and rechecked everything. That was actually my mistake. I accidentally mixed the 9 and 6 when I copied it from my handwritten math... But it did make me check all my math again, and new answer are $173,563.05 for annually. The monthly number remains unchanged though.