Fixed deposit
Maturity value, withholding tax and the effective annual rate.
Nothing you enter is sent anywhere
Interest paid
Gross interest
LKR 47,500
Withholding tax
LKR 2,375
Interest you keep
LKR 45,125
At maturity
LKR 545,125
What the rate really means
Nominal rate
9.5%
Effective annual rate
9.500%
Interest paid only at maturity does not compound, so the nominal and effective rates are the same. A bank paying monthly at the same headline rate would give you more.
The withholding rate is left editable rather than fixed, because it has changed repeatedly in recent years and applies differently to senior citizens and to certain account types. Take the current figure from your bank or the IRD and enter it, rather than trusting a default that may be out of date. Everything else here is arithmetic.