Frequently asked questions Can I estimate my income if I don't have all the information in my tax return? If all the information you need is not available until after you are due to file your tax return you can put your best estimate on the return. You must tell the Inland Revenue that the information is an estimate in the 'Additional Information' box. You must confirm the actual figures as soon as possible with your tax office. Can I complete my return after the January 31st deadline? How will I know if my tax affairs are being investigated? I think I paid too much tax, how do I get it back? © Taxes. All rights reserved.