Is there a function in Excel that will allow me to enter my current credit

card balance, the interest rate I'm being charged and the amount I wanna pay

every month and have Excel give me the rundown of how many months I must pay

that exact amount before my balance gets at 0.00$???

Or be able to calculate the exact amount I'm paying on interest day by

day?? For example:

Date Desc. Amount Bal.

2007/01/01 Balance 1000.00$ 1000.00$

2007/01/01 Payment 100.00$ 900.00$

2007/01/02 Interest 0.65$ 900.65$

2007/01/03 Interest 0.65$ 901.30$

2007/01/04 Interest 0.65$ 901.95$

2007/01/05 Interest 0.65$ 902.60$

2007/01/06 Interest 0.65$ 903.25$

To compute "the exact amount" of interest on a daily basis, the

following should do the trick:

=b*(1+i/365)

where "b" is the previous balance (e.g. 900), and "i" is the nominal

annual interest rate (which might not be the same as the APR). Note:

in the US, lenders can use 366 instead of 365 in leap years.

As for the first part of your question, if all credit card debt worked

the same way (it doesn't!), NPER() might be the function you are

looking for. But beware of the assumptions built into NPER(), namely

that interest compounds at the same frequency as the payment (e.g.

monthly).

Moreover, beware that in real life, interest and balance may or may

not be rounded internally, even though they are invariably rounded on

periodic statements. Excel financial functions presume that nothing

is rounded.

Finally, daily interest may or may not be compounded on a daily basis

-- although for loans, I would expect that it is, if interest is

charged on a daily basis.

Assuming that the daily interest is compounded, the following might

provide the answer you want:

=roundup(nper(fv(i/365,d2-d1,0,-1)-1, p, -b), 0)

where "i" is the nominal annual rate, "d2" and "d1" are two payment

dates (not column references; sorry for the ambiguity), "p" is the

payment (round to the smallest legal tender of the realm, at least),

and "b" is the outstanding balance after the most recent payment (e.g.

900).

The expression "fv(i/365,...,-1)-1" computes the monthly rate when

interest is compounded daily. Alternatively, it can be written "(1+i/

365)^(d2-d1) - 1".

The last payment might be smaller than "p". It is difficult to

compute when interest is compounded at a different frequency than

payments (e.g. daily v. monthly). The following is one approximation

daily compound interest and monthly payments. But it can produce

substantial error over long periods of time and when the interest rate

is very high, because 7 months of the year have more than 365/12 days.

=fv(fv(i/365,365/12,0,-1)-1, n-1, p, -b))*(1+i/365)

where "n" is the result of ROUNDUP(NPER(....),0) formula above. This

last formula should be rounded up to the smallest legal tender of the

realm.

HTH.