Calculating interest drop when withdrawing money

billy-bob

Registered User
Messages
115
I'm pretty sure this is a dumb question, but here goes. How do I calculate how much interest I'll lose when I withdraw money from a savings account?

Say I have an account attracting 4% interest, paid annually on 31/12. So on 1/1/2011, I put in 1000 euro, that will earn about 40 euro in the first year (less dirt). The 1000 euro I put in in December will only earn about 3 euro. If I take out 1000 euro in December, "which" 1000 do they take? How is this usually calculated?

On a spreadsheet, I calculated how much interest the 1/1 deposit makes, how much interest the 1/12 deposit makes and how much negative interest the 2/12 withdrawal makes. Then add them all up?

Code:
01-Jan	1000	39.89
01-Dec	1000	3.18
02-Dec	-1000	-3.07
		40.00