Changing Retention times - Estimating capacity

I am trying to estimate the capacity I am going to need when changing the retention time on my Global Deduplication policy - Primary copy from 30 days to one year.

If I look at the capacity of the storage policy now, w/ the 30-day retention period, would multiplying that by 12 give me an accurate estimate on capacity I will need to keep that primary copy for one year?  Ex - Primary copy w/30-day retention period = 300GB - changing to 365-day retention period = 3.6TB ?