"swiftiie" wrote:
I have a personal loan of $12,000 (at an interest rate of
10.4% per annum) [...].
I know how to set up the first 4 columns for the
date/balance/interest/my repayments, but it doesn't coincide
with my bank statments. I think this is because interest is
calculated daily but added monthly. Is there a formula to
relate to this, rather than the interest added to the principle
on a daily basis?

One of the following formula's should come close. Which one
depends partly on whether "10.4% per annum" is the APR,
which already takes daily compounding into account, or the
nominal annual rate. It also depends on whether your lender
uses 360 or 365 to determine the daily rate. Both are common.

If 10.4% is the APR, try the following with 360 or 365:

=RATE(365,, -1, 1 + 10.4%)

If 10.4% is the nominal rate, try the following with 360 or 365:

=FV(10.4%/365, 365,, -1) - 1

That is just the daily rate. To compute the interest compounded
during a month, try:

=(PreviousBalance)
*((1 + DailyRate)^(ThisPeriodDate - PreviousPeriodDate) - 1)

Alternatively and perhaps easier to remember and understand:

=(PreviousBalance)
*(FV(DailyRate, ThisPeriodDate - PreviousPeriodDate,, -1) - 1)

Your lender may or may not compute the interest with
ROUND(...,2). It will be difficult to tell unless you have many
periods of statements from the lender to compare with.