Overdraft Interest Calculation


New Member
Hi all,

I have a general question just trying to wrap my head around overdraft calculations.

If I have an overdraft facility of €10K which I'm using say €9K (to leave a bit for interest accrued etc).
Interest rate is 10% and the interest is calculated daily (See 8.1) based on a 360 days year (See 8.4) but charged at quarterly (See 8.2).

I'm a bit confused as to how the actual calculation of the interest work.

I took KBC's terms as example, excerpt below in quote:


8.1 Interest will be payable on the cleared daily debit balance under the Facility at the rate indicated in the Schedule on the Letter of Sanction as varied from time to time. That is, allowance is not made for cheques, drafts or other credits lodged until value has been received or for credit interest accrued but not yet credited to the Account. The rate indicated in the Schedule to the Letter of Sanction is the KBCI Personal Overdraft Rate which is the reference rate for the purposes of the Facility. You can obtain details of the current KBCI Personal Overdraft Rate on our website, in any of our offices or by contacting us directly.

8.2 Interest will be debited to the Account quarterly in arrears (or at such other intervals as are notified to you from time to time) and on final payment.

8.3 The interest rate applicable to the Facility is a variable rate and will vary in amount from time to time. We will take such steps as we consider to be reasonable and appropriate to bring any such variation to your attention and, without prejudice to the generality of the foregoing, either written notice or statement of account sent to you or publication of by way of a notice in at least one national newspaper shall constitute reasonable and appropriate notice for these purposes.

8.4 Interest will accrue from day to day and be calculated on the basis of the actual number of days elapsed and a 360 day year and will be payable as well after as before any judgment or demand.

8.5 A surcharge (in addition to the standard rate of interest applicable to the Facility) will apply to any drawings under the Facility in excess of the Overdraft Limit and will be debited to the Account quarterly in arrears (or at such other intervals as we may from time to time notify to you) and on final payment. Our current rate of surcharge is set out in our Schedule of Fees and Charges booklet.

8.6 We reserve the right from time to time to increase the rate of surcharge if we determine that a higher rate is necessary to adequately compensate us. At the time any such increase is put into effect, the new rate will not exceed the rate then currently charged by us on excess drawings on accounts that it considers to be of the same type as the Account. Any variation in the surcharge rate will be notified in the same way as a variation in the interest rate. If you do not agree with the increase in the rate of surcharge you may terminate this Facility.
Lets say for ease of starting point, the overdraft was taken on the 1st of January.

1st Jan / Balance = €9,000 / Interest is €2.5 [*Derived from ((9000*0.1)/360)]
2nd Jan / Balance = €9,000 / Interest is €2.5
15th Jan / Balance = €9,000 - €4,500 (Lodgement) = €4,500 / Interest is €1.25
31st Jan / Balance = €4,500 / Interest is €1.25

The way I have worked the interest out is that the interest accrued from the first day's balance and the interest doesn't get added to the balance for the purpose of calculating the next day's interest. (i.e. Interest is calculated daily, set aside and only added together once every quarter).

Is this the right way of calculating it? or should I add the daily interest to the balance at the end of each day for the purpose of calculating interest for the next day and so forth. This part is not particularly clear.

Hoping someone can help clarify


New Member
Yes. I thought it was the other way, but someone corrected me here.

The interest is not charged on the interest until it is posted to the account.

Thanks Brendan for clarifying.

That would make calculation much easier and overall interest slightly less :) which is a good thing


Frequent Poster
It is the cleared balance - so not necessarily the balance shown on the statement/online