How rent is converted between weekly, fortnightly, and monthly
This tool works from a weekly rent figure, which is how residential rent is quoted in Australia and New Zealand and in some other markets. Every amount it produces is built from a daily rate: daily rent = weekly rent / 7. A fortnightly payment covers 14 days, so it is the weekly rent times two. A weekly payment covers 7 days and equals the weekly rent.
Monthly is the case where the arithmetic stops being tidy. The calculator charges the actual number of days in each monthly period, so a period covering 31 days costs daily rate times 31 and a period covering 28 days costs daily rate times 28. Each monthly payment is therefore slightly different. This is a deliberate choice: it keeps rent allocated to the days it covers with no drift.
Many agents instead use the formula monthly rent = weekly rent * 52 / 12, which produces one constant figure every month. That convention charges 365 days of rent over 12 equal instalments rather than matching each payment to its period. If your agreement uses it, the totals over a year will be close to what this tool shows but the individual payments will not match, so check which basis your agreement specifies.
How the rent increase is split across a payment period
When a rent increase takes effect in the middle of a payment period, that one payment covers days at both rates. The calculator counts the days in the period before the increase date and the days from the increase date onward, then charges each at its own daily rate: amount = old daily rate * old rate days + new daily rate * new rate days. It labels that row as a transition payment so it is easy to find in the schedule.
Periods entirely before the increase date are charged at the old weekly rate and labelled old. Periods entirely on or after it are charged at the new rate and labelled new. The summary panel picks out three specific rows for you: the last payment at the old rate, the transition payment, and the first full payment at the new rate, since those are the three amounts people most often need to check against a bank statement.
Take a fortnightly tenant paying 760 a week, increasing to 780 from 12 January, with coverage beginning 5 January. The first period runs 5 to 18 January, which is 7 days at the old rate and 7 days at the new. The payment is 760 + 780 = 1,540.00. The following period, 19 January to 1 February, is entirely at the new rate, so it is 780 * 2 = 1,560.00. The transition payment sits between the old regular amount of 1,520.00 and the new regular amount of 1,560.00, which is exactly what you would expect.
Arrears, credit, and what to pay right now
The days currently overdue field counts rental days not yet paid for, ending on today's date. The calculator multiplies that count by the current daily rate to get the overdue amount, then subtracts any credit or rent paid in advance that you enter. The result is the pay now figure: pay now = overdue amount - credit, floored at zero.
Suppose the tenant above is three days behind and holds 200 in credit. Three days at 760 / 7 is 325.71. Subtracting the 200 credit leaves 125.71 to pay now. Paying that clears rent through today, which is why the schedule then starts allocating rent from tomorrow forward with no gap.
If the credit exceeds the arrears, the pay now figure is zero and the leftover credit carries into the schedule. The calculator applies it to upcoming payments in order, reducing each one until the credit is exhausted, and the schedule shows both the gross amount for the period and the amount actually due after credit. That is the same order of application most agents use.
Why the payment date can create an overdue gap
Rent is normally payable in advance, meaning the money is due on or before the first day of the period it covers. The calculator checks this for every row by comparing the debit date with the period start date. If a debit lands on or before the day its period begins, the row is on time. If it lands after, the schedule is flagged and the summary names the first period where coverage starts before the money arrives.
This is the situation that quietly creates arrears in an otherwise well run tenancy. An automatic transfer set up a few days after the period begins means the tenant is technically behind on every single payment, permanently, by the same few days. Nothing bounces and no payment is missed, yet a ledger will show the account in arrears the whole time.
The fix is to move the automatic payment earlier once, absorbing a one off partial payment to close the gap, rather than to change the amount. The calculator helps by separating the two questions: the pay now figure closes the existing gap, and the on time check tells you whether the schedule you have set up will keep it closed.
What the schedule does not cover
The tool computes rent only. Bond or security deposit, water usage charges, utilities billed separately, break lease fees, and any agent charges are outside it. The currency selector changes the symbol used for display and nothing else; no conversion is performed and no local rounding rule beyond cents is applied.
The arrears calculation uses the current weekly rent for every overdue day, even if some of those days fall on or after the increase date. If your arrears span the increase, the overdue figure will be slightly understated, and the correct approach is to treat the days before and after separately.
It also assumes the increase is valid and has taken effect on the date you enter. Notice periods, frequency limits on increases, and the grounds on which an increase can be challenged are set by the tenancy law of your state or country and vary considerably. The schedule shows what the arithmetic produces from the dates you supply; whether the increase itself is properly made is a separate question for your local tenancy authority.