Timezone not works

[luispimenta]

I'm creating a booking via API and everything is working perfectly:

json sending:

`{

"attendee":

{

"name":

"Luis Pimenta",

"timeZone":

"Europe/Lisbon",

"phoneNumber":

"19996873333",

"email":

"xxx@gmail.com"

},

"start":

"2025-06-16T09:00:00",

"eventTypeId":

2386141

}

}`

and in return:

`"status":

"accepted",

"start":

"2025-06-16T09:00:00.000Z",

"end":

"2025-06-16T09:15:00.000Z",
`

but the calendar is creating 10 AM hours not 09 AM

it is adding extra daylight saving time even though I am already putting the correct time in the sending json, can you help me?

[dosubot[bot]]

Hi @luispimenta! I'm Dosu and I’m helping the cal.com team.

The issue is likely due to how the API interprets the start time you send. When you provide "start": "2025-06-16T09:00:00", the API treats this as 9:00 AM UTC, not 9:00 AM in Europe/Lisbon. Since Lisbon is UTC+1 in June (due to daylight saving time), the event appears as 10:00 AM local time on your calendar.

To get the correct time, you should send the start time in UTC that matches 9:00 AM in Europe/Lisbon. For June 16, 2025, 9:00 AM in Lisbon is 8:00 AM UTC, so your payload should be:

"start": "2025-06-16T08:00:00Z"

The API always expects the start field in UTC, and then uses the attendee's timezone for display and notifications. The codebase uses the dayjs library for these conversions and normalizes all times to UTC internally, which can cause confusion if the input time isn't already in UTC for the intended local time reference.

If you want to automate this, convert your local time to UTC before sending it to the API. That should resolve the 1-hour offset you’re seeing.

To reply, just mention @dosu.

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[luispimenta]

@dosu But this is not correct, if I send one hour less, the return of the API will also be one hour less, and I use the return of the API to inform the customer the time that was actually scheduled, so how do I have to treat the shipping? Once you have the return, do another treatment to inform the user, this can give many problems, You have to have a way to send correct in the API, and the creation and the return already includes the time or summer time

[dosubot[bot]]

The cal.com API always stores and returns booking times in UTC, regardless of the attendee's timezone or daylight saving time. When you send "start": "2025-06-16T09:00:00", the API treats this as 9:00 AM UTC, not 9:00 AM in Europe/Lisbon. That's why you see a 1-hour shift during DST.

To avoid this, you need to convert your local time (Europe/Lisbon) to UTC before sending it to the API. For example, 9:00 AM in Lisbon on June 16, 2025 is 8:00 AM UTC, so you should send "start": "2025-06-16T08:00:00Z". The API will return the time in UTC, and you should convert it back to the user's local time for display.

There is currently no way to have the API interpret or return times in a local timezone automatically—all conversions must be handled on your side. This is a consistent design choice in the codebase and applies to all booking creation and retrieval endpoints see implementation.

If you need help with code to convert between UTC and local time (including DST), let me know your tech stack and I can provide an example.

To reply, just mention @dosu.

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