Why are my events one hour off?

Usually daylight saving or a time zone mismatch: the spreadsheet, the script project or the calendar is set to a different zone, or the time was converted with a fixed offset like GMT-6 instead of a named zone like America/Chicago.

Where do I set the spreadsheet time zone?

In Google Sheets, File → Settings → General → Time zone.

Guides › Wrong times

Events from Google Sheets show the wrong time in Google Calendar

The sheet says 9:00 AM; the calendar says 8:00 or 3:00 PM. Here are the six usual causes, in the order to check them.

1. The spreadsheet's time zone is wrong

Sheets turns a date and time in a cell into a moment in time using the spreadsheet's own time zone. If the file was created by someone elsewhere, or a template from another country, it may be set to a different zone. Check: File → Settings → General → Time zone. Changing it fixes new syncs; already-created events need a resync.

2. Dates are text, and a script parses them

A cell can look like "12/7/2026 9:00" and still be text. Scripts that do new Date(text) read it in the script project's time zone (set in appsscript.json), which may differ from the spreadsheet's. Text can also be read month-first or day-first depending on locale. Fix: make the cells real dates (Format → Number → Date time), or parse with Utilities.parseDate(text, spreadsheetTimeZone, 'M/d/yyyy H:mm').

3. Time-only cells become December 30, 1899

A cell with just "06:00" is stored as a time on Sheets' day zero, December 30, 1899. Used directly as an end time, it puts the event in 1899 or makes it fail. Historical time zone rules for 1899 can also shift it by odd amounts of minutes. Fix: combine the date and time first (=A2+B2), or in a script copy the hours and minutes onto the start date, adding a day if the end time is earlier (overnight shifts).

4. The calendar is shown in a different time zone

The event may be right but displayed in your Calendar's time zone, which follows your device when you travel. Check: Google Calendar → Settings → General → Time zone. Open the event: if it shows the right time with a zone label, it's a display setting, not a wrong event.

5. Daylight saving and fixed offsets

Events right in summer but an hour off in winter (or the reverse) almost always come from a fixed offset such as GMT-06:00 or -06:00 in a script, or from adding 24 hours to move to the next day across a clock change. Fix: send the wall-clock time plus a named zone ({dateTime: '2026-12-07T09:00:00', timeZone: 'America/Chicago'} with the Calendar API), and add days on the calendar date, not as 24-hour blocks. Watch for times that don't exist: 2:30 AM on the spring-forward night.

6. CSV import uses the calendar's time zone

Google Calendar's CSV import has no time zone column; it reads times in the time zone of the calendar you import into. If that calendar's zone differs from your sheet's, everything shifts. Check: the target calendar's settings → Time zone, before importing.

How Calendrow handles it: it reads each cell as the wall-clock time in your spreadsheet's time zone (or one you pick), sends it to Google Calendar with that named zone, shows the resolved time in the preview before writing, flags text that only looks like a date, rolls overnight end times to the next day, and handles the spring-forward gap. See how it works.

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