Unexpired basis

Hi, I am struglling to understand the apportionment for unexpired basis. Do you have a formula for the time fraction?

I understand that the basis narrows linearlly, but when trying Alecto Co they apportioned the basis as 2/6.

$22m in 4 months’ time on 1 May 20X2, expecting full repayment 9 months from now. Choose June futures.

My understanding for the numerator is 1 May – 30 Jun = 2 months unexpired

But why would the denominator be 6?

Thanks!