Donations made during 2018 go on a 2018 tax return; donations made in 2019 go on a 2019 tax return, etc.
If you make the contribution by credit card, it is considered made on the date that you charge it to the card, even if you don't pay the bill until the following year. If you make the contribution by mailing a check, it is considered made on the date that you mail the check. To avoid any disputes in case the IRS questions your contributions, it's a good idea to make the contribution early enough to make sure that the receipt from the charity shows the correct year.
also don' t forget you need a receipt from the org if contribution over $250 showing
1. The amount of any money contributed and a description (but not value)
of any property donated.
2. Whether the organization did or
didn’t give you any goods or services in
return for your contribution. If you did
receive any goods or services, a description and estimate of the value must be
included. If you received only intangible
religious benefits (such as admission to
a religious ceremony), the organization
must state this, but it doesn't have to describe or value the benefit.