Drip feed calculator

[georged3rd]

I'm looking to drip feed 24k from a high interest instant access account into 2 regular savers at 1k per month each over 12 months.

Calculating the interest from the regular savers is straight forward (i.e. use the calculators on the banks' websites or use the Future Value calculator here; http://www.askaboutmoney.com/clubman/CompoundCal.htm#rjava2)

But calculating the interest from the instant access account isn't so easy (for me anyway, maybe not for others here).

Taking KBC's Smart Access Instant Savings account as an example. I've tested formulas such as this (and other variations)
11k for 1 month; 11000 * .023 = 253.0 * .55 = 139.15 /12 = 11.5958 * 1 = 11.5958
10k for 2 months; 10000 *.023 = 230.0 * .55 = 126.5 /12 = 10.5417 * 2 = 21.0834
And so on...but I know the above formula is wrong based on the sum (e.g. the sum is more than 12k at 2.3% for 1 year with no drip feeding).

Does anybody have a correct/reliable formula or link to a calculator for this?

 

[RichInSpirit]

Not sure if are able to use a spreadsheet such as Excel, Google docs, Open Office.?
Just break your calculation's down into a month per row like you've done and it should be simple enough using simple maths.
Also for mortgages and loans anyway there's a built in function in Excel for working out almost anything to do with compound interest Loans.
There could be a similar function for interest on deposits.

 

[georged3rd]

Hi Richspirit, thanks. I can use Excel etc or do it manually like above but its really the formula that I need to ensure is correct rather than the tool itself.

Can anybody with experience of calculating interest returns from drip feeding confirm where I'm going wrong with the formula used in the OP?

 

[vandriver]

You need to use the 12th root of the interest rate for an accurate result.(12 th root of 2.3%(1.023) per year is 1.001896754))
So 1000 euro for a month would return 1001.896(less prsi dirt)
Of course,the banks credit interest daily,so you could find the 365th root of your interest rate and multiply up for the number of days in the month!