Ask ten portable toilet operators how they bill and you will hear "every 28 days" from most of them, "monthly" from a few, and "it depends on the customer" from the ones who have been doing it longest. All three are right. The cycle is a business decision, and the wrong decision is not picking 28 or 30, it is having rate cards on one and the company on the other without noticing.
Why 28 days is the industry default
A portable toilet on a construction site is serviced once a week. Four weeks is 28 days, so a 28-day cycle is four visits, every time. The invoice says "4 services" and it is always true. A calendar month is four visits in February and sometimes five in March, which either means a variable invoice or a flat rate that is secretly cheaper in long months.
The other reason is arithmetic. 365 days is thirteen 28-day cycles plus one day. Thirteen invoices a year at a $100 cycle rate is $1,300; twelve monthly invoices at the same number is $1,200. The 28-day company is not charging more per week; it is charging for every week.
When calendar months are right
Three kinds of customers want a monthly invoice:
- Municipalities and school districts. Their budgets are monthly, their purchase orders say "per month", and an invoice for May 3 to May 30 confuses accounts payable. See getting paid by municipalities.
- Large commercial accounts with a corporate AP department. Same reason. Thirteen invoices a year breaks their accrual.
- Long-term residential or farm placements where service is monthly anyway, so the week-based argument does not apply.
The answer is a company cycle of 28 days with those customers set to calendar months individually. The software should let the customer's cycle override the company's.
The mismatch that costs money
Here is the mistake we see on real books. The company bills every 28 days. A rate card row is entered as "monthly" because that was the dropdown's default. The engine then does one of two things: it bills that row at the monthly rate over a 28-day window (the customer pays for 30 days of service and gets 28), or it bills the calendar month containing the cycle start, and the invoice is a different length from every other invoice the customer gets.
Either way the customer notices before you do. The fix is a rule: a new rate card row defaults to the customer's cycle, and anything on the other period is flagged. In PortaPro a new row on a 28-day customer is per 28 days, and the nightly Billing Health sweep lists any row whose period does not match. Our post on auditing what billed covers that report.
Arrears or advance
Most rental billing is in arrears: the cycle ends, the invoice goes out. Municipal customers often need the invoice before the period starts, for PO approval. That is advance billing, and it is a per-customer setting, not a company one. A customer on advance gets next cycle's recurring charges plus a labeled true-up of last cycle's extra services on the same invoice.
Proration is the other half
Whatever the cycle, a unit that lands on day nine should be billed for the days it was there, and the next invoice should be the full cycle. If a tool cannot prorate to the day, you are either giving away up to four weeks on every placement or charging for days the unit was in the yard. The prorated first invoice walks through the math.
How to choose
- Default the company to 28 days if your service is weekly. Pick an anchor date and never move it.
- Put municipal and corporate accounts on calendar months, individually.
- Make sure every rate card row is on its customer's cycle.
- Audit every cycle. Thirteen times a year, a report that says what billed and what did not.
