Calculate a date based on another date

[Sandro Mancuso]

I'm creating a page that documents a launch plan.  There are several deliverables with due dates, and I want to make them all relative to the launch date.  Currently, I'm entering each one using the date macro, but each time the launch date changes (happens often, I'm working on that!), I have to manually change a dozen other dates.   With the audience for this file, a "-2W" type of indicator is not really working.

In short, I want to display date "X" once in a page, and then display a calculated relative date "Y" which is  "X-n" , where n is a number of days/weeks (or whatever, I don't care if I have to convert to seconds!)

In confluence cloud, what option (including plugins) do I have that can accomplish this? 

[Vasiliy Zverev]

Do you have a JIRA instance? You could create JIRA issues and then show results into Confluence

[Sandro Mancuso]

I was led to believe I can't add user macros on cloud.  I already thought of that - in fact, at my previous job we had an on-premise installation, but it had over 100X more employees .  A user macro is exactly how I solved this.  

We can't justify increasing the headcount by 1, and have 12.5% of staff just to admin JIRA.  I run into "Can't do this on cloud" probably once a week .

[Vasiliy Zverev]

It seems that you need a macro. 

main idea - find some html element where start date is stored and work with it with javaScript.

I would reccomend to organise all dates into a table and create a macro with param to add/minus of a Date into fixed row/line of this table.