From the query builder, you can report on how many days or hours an employee has accrued as at today. This option is called 'Pro-Rata Remaining Holidays' and can be found in the Employee Details area:
If the employee is already set up to accrue their holidays, this report wouldn't be required as their current entitlement will already show what they have already accrued.
If you give an employee a set amount for the whole year, this option will pro rata their entitlement from the beginning of the year (or their start date) to date.
For more information on the query builder and how to build reports, please see the linked article: http://help.peoplehr.com/reports-and-queries/creating-queries
The calculation for this is as follows:
Remaining = A x B/365 - C + D + E = ?
A = Entitlement
B/365 = Fraction of Year Worked
C = Leave Taken
D = Holidays Carried over
E = TOIL
Customer Services Team.