I purchased several different license agreements, at different times. How do I calculate main maintenance agreement costs? I understand that if I want to keep my support agreement and to have access to the latest versions, a new maintenance agreement is required for each license, after the first year. How do I go about calculating how much I have to pay?
Stepbystep guide
The maintenance agreement is calculated based on:
 The purchase date of your first license
 Future licenses are retroactively calculated to the date of the first purchase.
 The number of licenses you have
Let's take a concrete example. Suppose you have purchased the following licenses at the following dates (the actual date is rounded off to the next month, so 1/29/2016 will be 2/2016):
Purchase Date  Number of Licenses  Notes 

2/2016  2  Purchased two licenses in February of 2016 
9/2016  3  Purchased three license in September of 2016 
10/2016  3  Purchased three licenses in October of 2016 
Next, assume we're now in December of 2018 and we're trying to calculate the cost of the maintenance agreement for the 8 licenses we hold. This is done as follows:
 We calculate the cost based on the first license
 We retroactively adjust the dates of the other licenses to the purchase date of the first license
 All future license agreements are based off of the purchase date of the first license
This is best shown with this table:
Purchase Date  First Year (free maintenance)  Months to First Year Expiration  Total Retroactive Months  Full Years to Active  Licenses per Year  Total Maintenance  Notes 

2/2016  2/2017  0 months  0*2 = 0 months  2 years  2 licenses  4 years 

9/2016  9/2017  7 months  7 * 3 = 21 months  2 years  3 licenses  6 years 

10/2016  10/2017  8 months  8 * 3 = 24 months  2 years  3 licenses  6 years  
Total  45 months  16 years 
 
Total Maintenance: 16 years  45months = 12.25 years 

So the total maintenance on December 2018 is 12.25 years and the maintenance for all licenses will expire on 2/2019. After 2/2019 the maintenance cost is 8x per year because there are 8 licenses issued.
Remember:
 All maintenance licenses are retroactively calculated to the first year of purchase.
 Maintenance agreements always expire on the date of purchase of the first license.
 After the date of the first license expiration, the cost for each additional maintenance year, is multiplied by the number of licenses. For 8x licenses, the cost for each additional calendar year of maintenance is 8x years of maintenance.
 If you've paid any maintenance agreements already, they will be subtracted from the calculation. In the above example, if you paid one maintenance agreement, then the total maintenance will be 12.25  1 = 11.25 years.
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