Personal allowance waste

let’s ‘suppose’ you’ve a loss of 65000 in 14/15.

income/profit :

15/16 35000
14/15 4000
13/14 50000

now, offset against current income and previous yrs income

current yr: 4000 – (4000) = Nil. Personal allowance wasted.
carry back: 50000 – (50000) = Nil. PA wasted.
remaining loss = 65000-54000=11000
carry forward: 35000 – (11000)= 24000 – PA 10000= 14000@20% = 2800 (tax liability)

Now, if instead of relieving loss from 14/15, we relieve from 13/14 and 15/16 to save current yrs PA.

carry back: 50000 – (50000) = Nil PA wasted
current yr no loss relieved: 4000 – 4000 PA = Nil
remaining loss= 65000- 50000= 15000
carry forward: 35000- (15000)= 20000 – 10000 PA = 10000@20% = 2000 ( tax liability)

So you see it depends when to waste PA to save maximum tax.