HubSpot import date format errors

A HubSpot date import error means a date value in your CSV does not match the date format selected during HubSpot's import mapping step. Platform research for ReadyCSV found dates to be a top community-reported import failure source.

HubSpot accepts date values when they match the mapping choice: MM/DD/YYYY, DD/MM/YYYY, or YYYY-MM-DD. Do not assume HubSpot will understand every date that Excel or Google Sheets can display.

Spreadsheet tools often store and display dates differently from the raw CSV text. Values like Excel serial numbers, written-out dates, or dot-separated dates can look understandable to a human but fail HubSpot's import parser.

• Excel serial numbers such as 45292 are spreadsheet storage values, not HubSpot date strings.
• Written-out dates such as January 31, 2026 are not one of the three accepted CSV formats.
• Dot-separated dates such as 31.01.2026 may be common locally, but they do not match the listed HubSpot formats.

Pick one date format and make the entire column consistent before importing.

1. Decide which HubSpot mapping format you will use: MM/DD/YYYY, DD/MM/YYYY, or YYYY-MM-DD.
2. Convert every date-like value in the CSV column to that exact format.
3. Replace Excel serial numbers with real calendar dates.
4. Replace written-out month names with numeric dates.
5. Review a few rows manually after export to confirm the CSV text is what you expect, not just the spreadsheet display.

ReadyCSV flags date-like HubSpot columns when values do not match MM/DD/YYYY, DD/MM/YYYY, or YYYY-MM-DD. The warning calls out Excel serials and written-out dates as review risks before you upload to HubSpot.

The check runs locally in your browser against the current working copy. ReadyCSV does not upload your CSV, send date values to a server, or call AI to inspect the file.