Many financial institutions have disclaimers in the fine print of their agreement that they can take up to 3 business days to post a new contribution after they receive it and they report the posting date to the IRS. Ask the financial institution. This late I would personally visit the financial institution and get a printed dated receipt that specifies in writing that it is a 2018 contribution so that there will be no doubt.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
