How to set a specific subscription end date

I have scoured the support forum and checked the results so far. The most useful post was as follows:

>Hi @Donna,
>I hope you are well today and thank you for your question.
>This type of subscription isn't possible, you would need to code >something up to handle this.
>For more information on this see following threads.
>Best Regards,

I checked each of these threads but nothing useful showed up. One guy did some custom coding but did not share it.

What I found a little disappointing was the fact that support staff said they hadn't had many requests for this, yet it shows up on at least 100 posts. Further, they all agree that it is something easy to do. The issues seems to be that it is not specifically in line with the thinking that led to the plugin.

Here's what I want to do - provide an additional field in the subscription build that asks for a specific subscription end date. This would operate instead of the number of days from the date of subscription.

It cannot (as has been said) be too difficult, because the subscription has to calculate the date anyway. This field would just be used instead of the calculated result.

This is not as rare as you may think, and not just the province of "old organisations". It's a specific requirement for running scheduled courses or events. people enrol and the start date is fixed.

I have another tissue,but I'll raise that separately.

Thanks - JC