How to Build Date and Weekday Validation in Power Apps

This is particularly useful when an action should only be performed during business days.

6. Recommended Approach: Start the Week on Monday

For business applications, I recommend using:

Weekday(Today(), StartOfWeek.Monday)

With Monday as the first day:

Power Fx supports StartOfWeek.Monday and other StartOfWeek options for Weekday().

Check for weekdays

Now the formula becomes much easier:

Weekday(
    Today(),
    StartOfWeek.Monday
) <= 5

Check for weekend

Weekday(
    Today(),
    StartOfWeek.Monday
) > 5

This is my preferred approach for most business applications because the logic maps naturally to Monday = 1 through Friday = 5.

7. Useful Power Apps Patterns

Allow only Monday–Friday

Weekday(
    DatePicker1.SelectedDate,
    StartOfWeek.Monday
) <= 5

Allow only Tuesday and Wednesday

Weekday(
    DatePicker1.SelectedDate,
    StartOfWeek.Monday
) in [2, 3]

Allow only Monday and Tuesday

Weekday(
    DatePicker1.SelectedDate,
    StartOfWeek.Monday
) in [1, 2]

Check weekend

Weekday(
    DatePicker1.SelectedDate,
    StartOfWeek.Monday
) > 5

Display the selected day name

Text(
    DatePicker1.SelectedDate,
    "dddd"
)

Example result:

Friday

8. Practical Example: Invoice Approval

Suppose an Invoice Approval button should only work Monday–Friday.

Set the button's DisplayMode to:

If(
    Weekday(Today(), StartOfWeek.Monday) > 5,
    DisplayMode.Disabled,
    DisplayMode.Edit
)

You can also combine this with your existing approval conditions:

If(
    SelectedTask.Status.Value <> "Pending" ||
    Weekday(Today(), StartOfWeek.Monday) > 5,
    DisplayMode.Disabled,
    DisplayMode.Edit
)

Now the button is enabled only when:

1. The task is pending.

2. Today is Monday–Friday.
   

9. Practical Example: Date Picker Validation

Suppose users should not select a weekend date.

Use the Date Picker's validation logic:

If(
    Weekday(
        DatePicker1.SelectedDate,
        StartOfWeek.Monday
    ) > 5,
    Notify(
        "Please select a business day.",
        NotificationType.Warning
    )
)

This prevents users from selecting Saturday or Sunday for business transactions.

10. Today() vs Now()

A common question is when to use each function.

Microsoft notes that Today() and Now() use the current user's local time.

Best Practice

For most business applications, use:

Weekday(
    DatePicker1.SelectedDate,
    StartOfWeek.Monday
)

instead of relying on the default Sunday-based numbering.

It makes formulas much easier to understand:

<= 5

means Monday–Friday

> 5

means Saturday–Sunday

And:

in [2, 3]

means Tuesday–Wednesday.

Conclusion

Today() and Weekday() are small Power Fx functions, but they are extremely useful for implementing real-world business rules.

They can be used for:

• 📅 Date validation

• 🗓️ Business-day restrictions

• 🚫 Weekend blocking

• ✅ Approval rules

• 📦 Delivery-date validation

• 🧾 Invoice processing

• 📆 Appointment scheduling

• 🔄 Workflow conditions

For business apps, combining Weekday() with StartOfWeek.Monday generally produces the clearest formulas.