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Author Topic: New compound interest calculator  (Read 15286 times)

Patrick

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New compound interest calculator
« on: May 28, 2013, 11:24:43 pm »
I was looking for a compound interest calculator that would let me do two things. 1) Let me email the numbers around, and 2) show me the value of my future investment in today's money.

Well after quite some searching I couldn't find one so had to make my own. Here's some example figures I'm using to show a collegue how much money she'd have after 20 years if she gave up smoking and DSTV, and invested the savings on the JSE:
http://www.investorchallenge.co.za/calc_compound.php?initial_deposit=0&monthly_deposit=1225&yield=17&years=20&inflation=6

Hope you find it useful  :TU:
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Aragorn

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Re: New compound interest calculator
« Reply #1 on: May 29, 2013, 08:11:31 am »
Nice one Patrick. However, did you consider that the annual investment amount should also increase with at least the rate of inflation if not more? Considering that the price of smokes and DSTV subs also increase annually.
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Patrick

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Re: New compound interest calculator
« Reply #2 on: May 29, 2013, 08:20:07 am »
I did, and it does  :)
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Patrick

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Re: New compound interest calculator
« Reply #3 on: May 29, 2013, 11:30:50 am »
Oh and you can also use it to see how withdrawals would affect your balance by having a negative monthly deposit. So if our friend Orca wanted to draw R30k per month from a portfolio of R3m, and could guarantee 20% per annum, he'd be fine indefinitely ;D. Tax excluded obviously. Interestingly, at 19% the money will run out after 26 years...

http://www.investorchallenge.co.za/calc_compound.php?initial_deposit=3000000&monthly_deposit=-30000&yield=20&years=50&inflation=6
« Last Edit: May 29, 2013, 11:39:56 am by Patrick »
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Moonraker

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Re: New compound interest calculator
« Reply #4 on: May 30, 2013, 12:56:05 pm »
Here's another one, present value and all that. http://www.moneychimp.com/calculator/compound_interest_calculator.htm
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ptomli

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Re: New compound interest calculator
« Reply #5 on: June 07, 2013, 04:24:26 pm »
Can you explain your calculations for "Balance in today's money"?

It doesn't seem to match any formula we've been looking at, like "present = inflated / (1 + inflation)^years"

http://www.investorchallenge.co.za/calc_compound.php?initial_deposit=10000&monthly_deposit=&yield=0&years=2&inflation=10
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Orca

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Re: New compound interest calculator
« Reply #6 on: June 07, 2013, 06:16:16 pm »
Only just found this thread. Great calculator. Thanks Patrick. I can now plan my move more correctly if no Double Dips and Triple Dips etc ahead.
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Patrick

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Re: New compound interest calculator
« Reply #7 on: June 07, 2013, 07:30:01 pm »
Quote from: ptomli on June 07, 2013, 04:24:26 pm
Can you explain your calculations for "Balance in today's money"?

It doesn't seem to match any formula we've been looking at, like "present = inflated / (1 + inflation)^years"

http://www.investorchallenge.co.za/calc_compound.php?initial_deposit=10000&monthly_deposit=&yield=0&years=2&inflation=10

I was working backwards, from annual inflation to monthly inflation, but I've switched it now to the discounted present value formula as you've shown. It compares well with my back of the envelope calculations, let me know if you agree.

Quote from: Orca on June 07, 2013, 06:16:16 pm
Only just found this thread. Great calculator. Thanks Patrick. I can now plan my move more correctly if no Double Dips and Triple Dips etc ahead.
If all goes according to plan I'll come visit you on my boat in Portugal in 12 years time. Make sure you find the good fishing spots  ;D
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