Holiday Accrual Formula

Hi,

I am wondering if anybody can help with a holiday entitlement worksheet. All full time staff will have 20 days per year. However these are calculated on a monthly basis accruing 1.67 days per month.
I need a formula which will calculate this on a monthly basis also allowing me to deduct any days that may have been taken.
I also need to be able to make the formula work that if a member of staff leaves mid month eg: 15th Dec the formula will only calculate to that date and
not give me the 1.67 days as if they had worked until month end. If possible one excel sheet per month and I can copy each month. It's for 15 staff.

see example worksheet

Thanks in advance

Started 01st Oct 2017 Brought forward balance Accrued In Month Taken Balance

Joe Bloggs 01st Nov - 30th Nov 1.67 1.67 0 3.34

01st Dec - 31st Dec 3.34 1.67 2 3.01