Self-assessment payment requirement: tax, interest and fee must be paid and evidenced before filing a return to avoid default. Payment of tax, interest and fee must be made and evidenced before filing the return; payments, tax deducted or collected at source, and claimed reliefs and credits are taken into account in computing the payable amount. If pre-filing payment is short, it is adjusted first against fees, then interest, then tax. Interest for late filing is computed on tax declared in the return after allowable reductions, and separate interest addresses shortfall in advance tax. Payments made under self-assessment are treated as paid towards later assessments; non-payment renders the assessee in default.