See below for a formula that will dynamically return the first day of the current month.

CHOOSE works perfectly in this situation, because it allows arbitrary values for each day of the week.

We use this feature to roll back zero days when the first day of the month is a Sunday.

Conditional formatting rules for dynamic calendar

More details about this problem areprovided here.

If no value is found, it pulls a value from column H in the row above.

The same formula is used in all cells except B6.

Conditional formatting rules for dynamic calendar

Both rules are applied to the entire grid.

This is a better option than merging cells since it doesn’t alter the grid structure in the worksheet.

By default, WEEKDAY returns 1 for Sunday and 7 for Saturday, but this is configurable.

Conditional formatting rules for dynamic calendar

it’s possible for you to use the WEEKDAY function inside other formulas to check the day of week.

The values provided to CHOOSE can include references.

The TODAY function takes no arguments.

Conditional formatting rules for dynamic calendar

you’re able to format the value returned by TODAY with a datenumber format.

If you need current date and time, use…

Conditional formatting rules for dynamic calendar

Excel formula: Dynamic calendar formula

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Excel WEEKDAY function

Excel CHOOSE function

Excel TODAY function