Self Assessment Includes calculators for mortgages, loans, APR, payslips, VAT, stamp duty, company car and fuel benefits Simple calculators at your fingertips. Estimate your penalty for late Self Assessment tax returns and payments Get an estimate of how much you’ll need to pay in penalties and interest if you’ve missed the deadline for: sending your Self Assessment tax return; paying your Self Assessment tax bill. Lloyd’s calculator Work out adjustments under section 107 Finance Act 2000 when filing your Self Assessment tax return