Computing Overtime:

On Ordinary Days
Number of hours in excess of 8 hours plus 25% of hourly rate

On special day or regular holiday
Basic pay plus 30% of daily rate

On a rest day which also falls on a special day
Basic pay plus 50% of daily rate

A regular holiday (100% or double pay)
A regular holiday, which also falls as rest day (basic pay plus 160%)

Computing Night Shift Premium Where Night Shift is a Regular Work

On Ordinary day (110% x basic hourly rate)
On a rest day, special day, regular holiday (110% of regular hourly rate for a rest day, special day, regular holiday)

Computing Overtime on Night Shift

On ordinary day (110% x overtime hourly rate)
On rest day, special day or regular holiday (110% x overtime hourly rate for rest days, special days, regular holidays)

Computing 13th Month Pay

Total basic salary earned for the year exclusive of overtime, holiday, and night shift differential pay divided by 12 = 13th month pay.