Add the bill's period to its date, then add 3 days of grace; if the day falls on a public holiday, move to the preceding working day. Bill 1 → 14 August; Bill 2 → 3 November.

Rule: Due date = (Date of bill + period stated) + 3 days of grace. When the period is in months the same date of the later month is taken; when in days the exact number of days is counted (excluding the date of the bill). If the final day is a recognised public holiday, the bill is due on the preceding business day.

Bill 1 — 12th July, 1 month, 3 days grace