This is the time of year when procrastinators begin to fret about filing their income tax forms with Canada Revenue Agency by April 30. Of course, there are many reasons to file on time — such as avoiding expensive late fees and receiving tax refunds promptly. For retired people, the CRA has an extra reason to finish their taxes on time — the potential to boost their monthly income, or, on the flip side, to avoid a reduction in government payments. That's because the federal tax collector checks seniors' returns to see if they're receiving old age security (OAS) and eligible for a guaranteed income supplement (GIS). Employment and Social Development Canada estimates 10 per cent of eligible seniors didn't receive their GIS payments in 2016-17. Since then, the government has attempted to increase public awareness and reduce missed opportunities. For the poorest seniors with virtually no income besides the OAS, the GIS could be worth up to a maximum of $898 a month for single people and up to $540 per person for couples. OAS is currently worth about $600 a month per person for most people who meet Canadian residency requirements. Just because a senior receives GIS in a taxation year doesn't mean they don't have to file annually with the CRA.