A company can opt to receive interest gross and pay tax when doing the year end submission. The advantage would be use of the otherwise-deducted Dirt for a time.
The tax rate paid by a company on non-trading income was 25%. I'm not sure if that has gone up now.
If the company is controlled by 5 or fewer people then the deposit interest is subject to a further surcharge of 20% of the after tax income if that income is not distributed.
DIRT is a withholding tax not a tax in itself.
Interest €4,250
CT @25% = €1062.5
Surcharge = €637.5
Effectively making the tax rate 40%
Net €2,550
If the company has paid DIRT it can claim it as a credit against the above.
No, if Dirt had been paid that would be allowed as a credit against final corporation tax due. You don't pay both.
When Dirt was 20% companies were paying a further 5% on their interest income. I am not aware that the CT rate for interest income has increased from 25% but it would seem strange if not.