Outlook All-Day Events Show Up One Day Early in Google Calendar — the Fix

You block out Friday as an all-day event in Outlook. In Google Calendar it sits on Thursday. A three-day trip starts a day early and ends a day early; a birthday shows up the night before. Your timed meetings might be perfect — it's specifically the all-day ones that slide. There's a precise reason for that.

Why all-day events drift by a day

A correct all-day event in the iCalendar standard has no time and no time zone at all — just a date: DTSTART;VALUE=DATE:20260626. Every calendar app, anywhere on earth, shows it on the 26th. Nothing to convert, nothing to get wrong.

Outlook's published feed often writes all-day events differently — as a timed block running midnight to midnight, tagged with a Windows zone and no matching VTIMEZONE:

DTSTART;TZID="W. Europe Standard Time":20260626T000000

Google can't resolve W. Europe Standard Time, so it reads that midnight as UTC midnight. For anyone east of UTC, local midnight already happened the evening before in UTC terms — so Google parks the event on the 25th. West of UTC, the reverse. And right at a daylight-saving boundary, the start and end can resolve to different offsets, which is why a single all-day event sometimes stretches across two days instead of one.

Why Outlook can't fix this for you

There's no toggle in Outlook that changes how the feed encodes all-day events. The midnight-plus-a-Windows-zone format is baked into what Microsoft hands you, and the missing VTIMEZONE is the actual breakage. The repair has to happen in the feed: that Windows zone needs a real IANA name and a valid VTIMEZONE block, so the date resolves where it's supposed to.

The fix

That's exactly what CalConverter does. It swaps the Windows zone for a standard IANA zone (W. Europe Standard Time → Europe/Berlin) and adds a valid VTIMEZONE definition for it. Now that midnight resolves in a real time zone instead of UTC, the event stops jumping the boundary — Friday's all-day block lands on Friday.

Steps

1. Publish your Outlook calendar and copy the .ics link (where to find it).
2. Convert it with CalConverter.
3. Replace your existing Google or Apple subscription with the converted URL — remove the old one, or you'll keep seeing the wrong-day copies next to the corrected ones.

If only some all-day events are off

That's normal, and it's a clue. Events you created while Outlook was set to a different time zone — or that were imported from another system — carry a different TZID than the rest, so they shift while the others stay put. The conversion maps each event's Windows zone to its IANA equivalent, so they all resolve consistently instead of one-by-one.

If your timed meetings are also off by a fixed number of hours, that's the same root cause showing up differently — see Google Calendar shows wrong times for Outlook events.