Upgrade Plan - Renewal Date Has Changed And Value Goes Up

We have a member who renewed their membership (on Sunday) and then wanted to upgrade to the next level.

On (admin) upgrading today, their renewal date has changed, also, the value of the upgrade does not appear to be the difference between the two, minus 2 days, but it has increased the price slightly!

We do not get many upgraders, so have not noticed this before.

Don't understand. The value of what goes up? The plan they want to upgrade to is suddenly more expensive? Did they use a coupon to discount their previous purchase? Is prorating enable so it can prorate remaining value?

Sorry, to clarify:

They are 2 days into a 149 plan
They want a 199 plan
The upgrade cost 51.17?

'Prorate remaining value of this plan when upgrading' is set to 'yes', so I would have expected the upgrade cost to be 49/48...!

Are you applying tax? That seams like the only way it'd actually increase.

Yes, we are, but tax is applied to all membership levels.

It is almost as if it is increasing the price because of the first membership level being extended by 2 days (but that calculation would be 0.8x).

What would the price be of the 149 and 199 plans with tax added to them? It's supposed to take their final totalizers so any tax or static promotions applied are taken into consideration. It then has to determine how much value the amount of time they used is worth and subtract that. So it'd be something like the below.

( 199 + tax ) - ( ( 149 + tax ) - ( time value ) )

Most likely what's happening is they are saving money, but it's mostly on the tax since 2 days of a 149 plan is very little value depending on plan duration. For example if it's a 1 year plan then 1 day is only worth roughly 40 cents.. so at 2 days they're roughly at 148.20 of value. You subtract that from 199 and you're at 50.8. Factor in tax and it'll easily hit 51.17.