This report responds to a request from Senator Yuen Pau Woo to estimate the post-COVID cost of a guaranteed basic income (GBI) program, using parameters set out in Ontario’s basic income pilot project. PBO presents three estimates based on scenarios that phase-out the benefit by $0.50, $0.25 and $0.15 for each dollar of employment income for the last six months of 2020-21. Also, this report considers the provincial breakdown of the GBI cost. The total estimated gross cost of the defined GBI would range between $47.5 billion and $98.1 billion based on the three scenarios for the six-month period from October 2020 to March 2021. In addition, the report provides an estimate of the federal and provincial programs for low-income individuals and families, including many non-refundable and refundable tax credits that could be replaced by the GBI program. PBO estimates the potential offsets from repealing these measures would be just over $15 billion for the same period.