Quarter Days are often the dates specified in leases when the rent and any service charges are payable and they are:
Lady Day: 25th March
Midsummer Day: 24th June
Michaelmas Day: 29th September
Christmas Day: 25th December
Rent and service charges are often paid on the usual Quarter Days in advance, that is for example the rent due on 24th June is for the period from 24th June to 28th September inclusive. In some old leases payment can be in arrears, that is for example the rent due on 24th June is for the period from 26th March to 24th June inclusive.