Sec. 6511: Limitations on credit or refund
The start date for counting the Sec. 6501(a) assessment statute of limitation period also tells the taxpayer the general three-year statute of limitation for filing a refund claim under Sec. 6511(a). A claim for refund must be filed within three years from the date "the return was filed" or two years from the time the tax was paid, whichever is later (Sec. 6511(a)).
https://www.thetaxadviser.com/issues/2021/jan/taxpayer-dates-limitations-coronavirus.html
