Calculation mirror timeline duration


Is it possible to calculate a duration from a mirror column showing timeline ?

It seems that we can’t have date#start and date#end as a regular timeline column.


Hi @corentin.dalfarra !

You have the right idea but try this formula instead:

DAYS({Mirror#End}, {Mirror#Start})

If you renamed your mirror column, just replace the “Mirror” with your column name.

Hope this helps!

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Hello @jailynnlucidday ,

It works well thanks ! I was thinking that we could not use formulas with mirrored timeline column.

Have a great day,


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Hi everyone, my Timeline column is actually a kind of mirror column showing summary of subitems dates (show summary on Parent item). In this case the #Start or #End is not working. Anyone facing same issue?

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