The expression is:

div(sub(ticks(‘Date1’),ticks(‘Date2’)),864000000000)

example : div(sub(ticks(‘2019-05-13’),ticks(‘2019-05-04’)),864000000000)

so the output is will give us 9 days.

For this in Power Automate we can use “Compose” Action.

Output after running flow we will get:

Suppose if you want to use this in Apply to each Condition step from Get SharePoint items we must write expressions like :

div(sub(ticks(items(‘Apply_to_each’)?[‘DOBDate’]),ticks(formatDateTime(utcNow(), ‘yyyy-MM-dd’))),864000000000)

SharePoint or Excel date column: DOBDate