# Subtract Length from Modification Date

**URL:** <https://community.mp3tag.de/t/subtract-length-from-modification-date/52802>\
**Category:** Support\
**Created:** [April 12, 2021, 9:42am UTC](https://community.mp3tag.de/t/subtract-length-from-modification-date/52802 "2021-04-12T09:42:10Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![hammad9860](https://community.mp3tag.de/letter_avatar_proxy/v4/letter/h/cdc98d/32.png) [@hammad9860](https://community.mp3tag.de/u/hammad9860)\
**Post date:** [April 12, 2021, 9:42am UTC](https://community.mp3tag.de/t/subtract-length-from-modification-date/52802/1 "2021-04-12T09:42:10Z")

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Looking for quick help.  
I want to subtract Length of some m4a files from their Modification Date to obtain Creation Date. This can be done with exiftool (by subtracting Length total seconds from Modification Date seconds) but I've made a long Action Group in Mp3tag and want to done everything within it.

Example, one file has following Modification Date and Length:

08/11/2020 12:41:39 pm (%\_file\_mod\_datetime%) and the length of this file is 01:22:51 which equals to 4971 seconds (%\_length\_seconds%).

How do you minus those seconds from that date.

I just don't know how to do it within Mp3tag. Help please!

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**Author:** ![ohrenkino](https://community.mp3tag.de/user_avatar/community.mp3tag.de/ohrenkino/32/4843_2.png) [@ohrenkino](https://community.mp3tag.de/u/ohrenkino)\
**Post date:** [April 12, 2021, 11:33am UTC](https://community.mp3tag.de/t/subtract-length-from-modification-date/52802/2 "2021-04-12T11:33:33Z")

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See the help on [arithmatic scripting functions](https://docs.mp3tag.de/scripting/#arithmetic-functions)

But once you have done the calculation - what are you going to do with it? MP3tag does not modify the file dates.

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<div class="post-metadata">

**Author:** ![hammad9860](https://community.mp3tag.de/letter_avatar_proxy/v4/letter/h/cdc98d/32.png) [@hammad9860](https://community.mp3tag.de/u/hammad9860)\
**Post date:** [April 12, 2021, 4:43pm UTC](https://community.mp3tag.de/t/subtract-length-from-modification-date/52802/3 "2021-04-12T16:43:57Z")

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I didn't know Mp3tag wasn't able to change dates. How did I miss that 😄

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**Author:** ![system](https://community.mp3tag.de/uploads/default/original/2X/c/ce7035d426cb755a7916793326d23b465222a407.png) [@system](https://community.mp3tag.de/u/system)\
**Post date:** [May 12, 2021, 4:44pm UTC](https://community.mp3tag.de/t/subtract-length-from-modification-date/52802/4 "2021-05-12T16:44:14Z")

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