Donations to be receipted for a year must be RECEIVED by the charity in the same year, and that receipt must be evidenced.
If you mail a receipt or date a cheque in a year and mail it late in the year, but the mail is received in the new year, we can only receipt the item for the prior year if the return address is on the envelope and a postmark on the envelope must show that it was mailed in the prior year. If the postmark is not there, or legible, then the item cannot be receipted for the prior year. It is not uncommon for the postmark not be there or dated.
The best-case scenario, if the donation is not being handed to the charity by mid-December, we recommend an electronic donation be processed via CanadaHelps: https://www.canadahelps.org/en/
Please note, dropping off a cheque dated for the current year to a charity on December 30th does not make it eligible for a tax receipt that year if the charity is closed and staff are not there to accept and process the item.
Please see further FAQ on the Canada.ca website: