Pro-rated leave calculation - excel-formula

Question

Is there any formula that I can transform to excel language for the following condition:
He joined in on 1st Aug 2019
1 Aug 2019 to July 2020 is his 1 year
on his second year we count from Aug 2020 to July 2021 is his 2nd year.
So for his pro-rated leave, we need to do a manual calculation by breaking apart the months due to different entitlement based on length of services.
Why we calculate like this is becos on 1st year he is entitled to 10 days leave but 2nd year onwards he is entitled to 12 days leave and Max is 16 days leave upon working on the 5th year.
Jan 2021 to July 2021 = 7 months/12*10 =5.83 (Multiple 10 is becos Jan 21 - Jul 21 is his 1st Year)
Aug 2021 to Dec 2021 = 5 months/12*12 =4.99 (Multiple 12 is becos Aug 21 to Dec 21 is his 2nd Year)
Next we will add up 5.83 + 4.99 = 10.82 (Round down to 10.5)
currently, im using this formula to tabulate their leave entitlement based on their joined year.
=IF([#[No. of years Joined]]=0,16,IF([#[No. of years Joined]]<2,16+[#[No. of years Joined]]-0.5,20))
Leave entitlement based on Job grade and length of services
However, this formula doesnt achieve the correct leave entitlement.
Current System

Answer 1

Check out the solution which I have created.
In the image the following are the formulas which I have used
In Cell C7
=DATEDIF(B7,DATE(2022,1,1),"M")
In Cell D7
=(QUOTIENT(C7,12)+1)*12-C7
In Cell E7
=12-D7
In Cell F7
=VLOOKUP(ROUNDDOWN(C7/12,0),$B$1:$C$4,2)
In Cell G7
=VLOOKUP(ROUNDUP(C7/12,0),$B$1:$C$4,2)
In Cell H7
=D7/12*F7+E7/12*G7
I hope this is your requirement.
Of course you can extend this table to include various paygrades (by having another lookup column) and extend it to further years too (by changing the formula in C7).