> You invest $200 in a savings account twice per month. The account pays 3.4% interest and is compounded monthly. What is

You invest $200 in a savings account twice per month. The account pays 3.4% interest and is compounded monthly. What is

Posted at: 2014-12-05 
Note: my calculator "remembers" all the digits after the decimal point, e.g. no rounding, so if you simply "plug" the numbers I've given below you might come up with slightly different results.

1.) Convert the stated rate to an annual compound rate

0.034 / 12 = 0.0028333

(1.0028333^12) - 1 = 0.034534, or about 3.453%
2.) convert this to a "stated rate" for 24 periods per year...

[1.034534^(1/24)] - 1 = 0.00141566 < this is the stated rate that, when compounded over 24 periods, gives you the same annual compound rate as compounding monthly (as in #1)

Another way to look at this is (probably a simpler way): What semi-monthly rate, when compounded, gives you the equivalent of the monthly stated rate?

monthly stated rate: 0.034 / 12 = 0.0028333

the semi monthly stated rate, that when compounded for 2 periods gives you the monthly state rate:

[1.002833^(1/2)] - 1 = 0.00141566

check math: [1.0014566^2] - 1 = 0.0028333
3) use the semi-monthly stated rate you've calculated (in #2 or just above) in the FV ordinary annuity formula...

FVoa = PMT [((1 + i)^n - 1) / i]

n = 24 * 5 = 120

= 200[(1.00141566^120) - 1) / 0.00141566]

= 200[130.694766]]

= $26,138.95

I hope I explained this well enough for you to understand it.

When you invest twice $200/ Bank will take only the minimum balance in the month for interest payment. So first month they may take 200 next month 600 + interest of first month. So the formula cannot be applied.

I would like to know where & by who do you get 3.4% interest ?

I know how to do future problems and I know you have to divide the interest by 12 because it's monthly and multiply the number of periods by 12. What is throwing me off is the $200 twice a month. I have never had a problem where I was asked to find the future value where someone invested money twice per month. If anyone could help me I would greatly appreciate it.