Calculating difference between two date custom fields in Trello

[Manjula Madineedi]

I am looking if there is a way to calculate the difference between two date custom fields using Butler? Ex: I have 'Start Date' and 'Completion Date' as 2 custom fields and if I want to know the duration of the task, want to write a Butler rule which will calculate the difference of these 2 dates and return in another custom field of 'Task time'. Can someone help?

[PROYECTOS DC SPAIN]

I'd like to know the answer as well. I have the same message. Thanks!

[Vero Rivas]

Hi @Manjula Madineedi 

   Look at this post, maybe can help you

   https://help.trello.com/article/1159-arithmetic-in-date-variables

Cheers

[Manjula Madineedi]

Thanks for sharing @Vero Rivas . But that doesn't work for me. Here is the rule I wrote:

when a card is moved into list "Completed", set custom field "* Hours Task Time" to "{{%Completion Date}-{%In Progress Start}}"

When I checked the Command log of the rule, it had this message -- "NaN" is not a valid numeric value.

I am not sure what's wrong in the above rule..

[Kelsey Lee]

I'd like to know the answer to this as well. I have the same custom field set up with start date. Trello seems to have updated the calendar to allow start and end dates. That's the only way I've been able to get the timeframe between start and end.