This is my first ED Visa and I have a question:

Today (a monday) I was supposed to report at immigration. However, when I got at the immigration office in Jomtien, it was closed due to a holiday.

Now what? Is tomorrow still ok?

If I not ok, what's the charge?

Be aware in the future to give yourself more time to check in. A week early is encouraged. Most likely you will be fined per day being late, however I am unaware of the amount.

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As today was a holiday you should be OK going tomorrow.

Thanks for the answers.

Today I went to the immigration office, and didn't have any trouble getting the 90-day report done. Nothing was charged.

I was even told by another farang in the queue that there is a tolerance after the day that the paper says, like a week or so.

Were you doing an address report or a new 90 day ED visa extension of stay - entirely different things. Many people here on ED visa have to extend every 90 days using a TM.7 and 1,900 baht. For that next workday is allowed. For 90 day address reports up to 7 days late (from due date) is allowed.