Power Automate provides functions to add time based on each of the units. For example, you can use the "addSeconds" function to add only seconds, but the "addToTime" function can provide a lot more flexibility since you define the unit that you want to add.

Usage

It follows a simple pattern.

1. Date
2. Number to add/remove
3. Time unit to add
4. (Optional) Date Format

The supported time units are: "Second", "Minute", "Hour", "Day", "Week", "Month", and "Year". Make sure you capitalize them exactly as shown in the documentation.

Here's a simple example:

addToTime('2019-10-28T10:10:00Z',10,'Second','yyyy-MM-ddTHH:mm:ssZ')

will return

'2019-10-28T10:10:10Z'

Looks quite straightforward, right? Positive numbers add time, and negative numbers subtract it. You can also use the "subtractFromTime" function for subtraction if you prefer to keep things explicit.

Please be aware that in the reference material, Microsoft names objects like '2019-10-28T10:10:00Z' as timestamps. I prefer calling them "Date" to avoid confusion with the UNIX timestamp, commonly used in APIs, to represent the number of seconds elapsed since Jan 01, 1970 (UTC).

Edge Cases

Adding months, weeks, and years

There are no "addMonths", "addWeeks", or "addYears" functions in Power Automate. If you need to add any of these units to a date, the "addToTime" function is the right way to do it. Here's an example adding 3 months:

addToTime('2019-10-28T10:10:00Z',3,'Month','yyyy-MM-ddTHH:mm:ssZ')

will return

'2020-01-28T10:10:00Z'

This is much simpler than trying to calculate the number of days in each month and using the "addDays" function.

Limitations

Unlike SharePoint and Power Apps, there's no limitation to the date that you can use. You can do things like:

addToTime('1000-12-30T00:00:00Z',10,'Year','yyyy-MM-ddTHH:mm:ssZ')

and you'll get

1010-12-30T00:00:00Z

Dates behave like you're expecting them.

Recommendations

Here are some things to keep in mind.

Always include the format

Even if the value is optional, always define it. The default format includes fractional seconds and time zone information that you probably don't need, and the date provided may not be in the same format returned or even trigger errors. You can define a single format specifier (for example, "o") or a custom format pattern (for example, "yyyy-MM-dd"), so pick your favorite, but be sure to define it.

Prefer individual functions when they exist

When an individual function exists, like the "addSeconds" function, I prefer using it since it makes the formula quite clear and shorter. But for months, weeks, or years, the "addToTime" function is your only option.

Use "getFutureTime" and "getPastTime" for the current timestamp

If you just need to add or subtract time from the current timestamp, check out the "getFutureTime" and "getPastTime" functions. They do the same thing but use the current time automatically, so you don't need to provide a date.

Your Questions

Replacing the year while keeping the day and month

Paul asked a great question in the comments: is it possible to keep the same day and month from a date but always set the year to 1970? For example, converting 03.11.2000 to 03.11.1970. You can't simply subtract 30 years because the original year might change.

The trick is to calculate the difference between the original year and your target year, then use the "addToTime" function to adjust it:

addToTime('2000-11-03T00:00:00Z', sub(1970, int(formatDateTime('2000-11-03T00:00:00Z', 'yyyy'))), 'Year', 'yyyy-MM-ddTHH:mm:ssZ')

will return

'1970-11-03T00:00:00Z'

The "sub" function calculates 1970 - 2000 = -30, and the "addToTime" function subtracts those 30 years. Since we're calculating the difference dynamically, this works regardless of the original year. Replace the hardcoded date with your dynamic value and it will always land on 1970.

Keep in mind the month-end clamping mentioned above. If your original date is February 29 (a leap year) and your target year is not a leap year, the day will silently shift to February 28. If that's a problem, you can build the date as a string instead:

concat('1970-', formatDateTime('2000-11-03T00:00:00Z', 'MM-dd'), 'T00:00:00Z')

will return

'1970-11-03T00:00:00Z'

This approach skips the "addToTime" function entirely and just swaps the year in the string. However, if the original date is February 29 and the target year is not a leap year, this will generate an invalid date and trigger an error. So pick the approach that best fits your scenario: silent clamping with "addToTime" or an explicit error with "concat".

Final Thoughts

The "addToTime" function is a flexible way to manipulate dates in Power Automate by letting you choose the time unit to add. It's especially useful for adding months, weeks, or years, since there are no dedicated functions for those units. Just keep the month-end clamping behavior in mind if you're working with dates at the end of the month, and you'll be fine.

Sources

Microsoft's "addToTime" Function Reference

Back to the Power Automate Function Reference

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