I worked it month by month in Excel and working to 10 dp.

The screen shot below shows the last few months. I deliberately 'overshot' in case one should be counting 59 or 61 months.

Small rounding errors will build up over 60 iterations so I claim my answer is the most accurate.

Bob

]]>Welcome to the forum.

I don't know it either but I'll have a go at working it out.

Firstly I want to work out a monthly interest multiplier that is equivalent to 10% per annum

The per annum multiplier would be x 1.1 so to get a per month multiplier:

Now work through a few months to establish a pattern.

Start of month one

End of month one

Start of month two

End of month two

Start of month three

End of month three

So after 60 months

Using the formula for the sum of a GP

In the screen shot below I have worked through 3 months like this and then used the formula to check the formula gives the same value.

http://www.mathsisfun.com/algebra/seque … etric.html

As I've just made this up it would be great to know that a financial calculator gives the same results.

NEXT DAY EDIT:

I tried http://www.thisismoney.co.uk/money/savi … lator.html

It made it £34846.68 whereas my formula made it £34727.28 (using Excel)

This calculator only accepts interest rates to 2 dp so it is not clear whether my formula is wrong or whether their's is insufficiently accurate.

I'll try to find a more accurate one.

A LITTLE LATER:

http://www.calculatorweb.com/calculator … calc.shtml

gives 35877.46

Bob

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