Why EIR matters
A flat rate is commonly advertised against the original principal, while repayments reduce the outstanding balance over time. Processing fees and the repayment schedule can make the real annualised cost higher than the headline figure.
EIR is useful for comparing offers, but it is not the only decision factor. Monthly affordability, total payable amount, late charges, early repayment terms and lender legitimacy also matter.
What to enter in a comparison
Use the principal, stated interest method, processing or admin fee, tenure and repayment frequency from the offer. Compare two offers at the same amount and tenure where possible. Treat any online calculator as illustrative and use the lender’s written agreement for the final figures.
Do not optimise only for the rate
A longer tenure may reduce the monthly instalment but increase total interest. A low rate with a large fee may cost more than a slightly higher rate with lower fees. Choose the offer that is affordable and clear, not simply the one with the smallest advertised number.