Billing Cycle Calculator

Every 28 days vs once a month

A 28-day cycle is four weeks, so every billing date falls on the same weekday. A month has 28 to 31 days, so a 28-day cycle runs ahead of the calendar: 13 cycles of 28 days are 364 days, one day short of a 365-day year. That is why a 28-day cycle usually gives 13 billing dates a year where monthly billing gives 12, and why the day of the month moves back by 1 to 3 days after every month longer than 28 days.

Both schedules below start on 5 Jan 2026. The 28-day dates are all Mondays; the monthly dates stay on the 5th:

In 2026 the 28-day schedule has 13 billing dates and the monthly one has 12. The next 28-day date is 4 Jan 2027, 1 day before the monthly date of 5 Jan 2027. A calendar year has 14 charges on a 28-day cycle only when the first one falls on 1 January (or, in a leap year, on 1 or 2 January).

Every 30 days is not monthly either. 12 × 30 = 360 days, so a 30-day cycle also moves 5 or 6 days earlier in the calendar each year. If you mean "once a month", choose Monthly on day D.

Monthly price vs 28-day price

Because a year holds 13 charges on a 28-day cycle and 12 on a monthly one, the same price per cycle does not give the same yearly total. The arithmetic, for a monthly price of 100.00:

• Monthly: 12 × 100.00 = 1,200.00 a year.
• Same price every 28 days: 13 × 100.00 = 1,300.00 a year, one extra charge.
• Same yearly total: 28-day price = monthly price × 12 ÷ 13 = 92.31 (rounded to cents); 13 × 92.31 = 1,200.03.

Plain arithmetic on a year with 13 charges, not an estimate. In a year with 14 charges the totals are one charge higher.

Billing days 29, 30 and 31 in shorter months

Not every month has a 29th, 30th or 31st. This calculator's rule, a design choice of this tool: when the month does not have the billing day, the billing date is the last day of that month, and the next month goes back to the chosen day. Dates are always counted from the billing day, never from the previous date, so one short month does not pull every later date back.

Monthly on day 31, starting 31 Jan 2026:

• 31 Jan 2026 (Saturday)
• 28 Feb 2026 (Saturday)
• 31 Mar 2026 (Tuesday)
• 30 Apr 2026 (Thursday)
• 31 May 2026 (Sunday)
• 30 Jun 2026 (Tuesday)

Quarterly and yearly cycles use the same rule with the day of the first billing date: a yearly cycle that starts on 29 February bills on 28 February in years that are not leap years. Other billing systems may handle these days differently, so if a contract or a provider sets the dates, go by theirs.

Billing dates in a spreadsheet

With the first billing date in cell A2:

• Every 28 days: =A2+28 in A3, then fill down. Microsoft's Excel help on adding days: "You can enter a negative number to subtract days from your start date, and a positive number to add to your date."
• Monthly: =EDATE(A2,1) gives the date one month later. Microsoft: "Use EDATE to calculate maturity dates or due dates that fall on the same day of the month as the date of issue." The syntax is EDATE(start_date, months) in Excel and in Google Sheets.
• Month-end days: count every row from the first date, for example =EDATE($A$2,1), =EDATE($A$2,2) and so on (or =EDATE($A$2,ROW()-2) filled down), not from the row above. In our test in Microsoft Excel, EDATE of 31 Jan 2026 plus 1 month returned 28 Feb 2026 and plus 2 months returned 31 Mar 2026, but chaining from the row above turned 28 Feb 2026 into 28 Mar 2026.
• Due date of each invoice: =A2+30 in the next column for Net 30. Format date cells as dates.

Sources: Microsoft Support, EDATE function and Add or subtract dates; Google Docs Editors Help, EDATE. Checked 25 Sep 2026. The month-end results come from our own test in Excel on 25 Sep 2026; neither help page describes that case.

Credit card and utility billing cycles

This calculator is for billing cycles you set yourself, such as a retainer or a subscription you invoice. For a credit card, phone or utility account, the provider's statement shows the actual cycle dates and the payment due date.

Invoicing on these dates

Make each invoice in the free invoice generator on its billing date. The generator does not schedule, repeat or send invoices, so there is nothing to set up in advance: on each date, set the invoice date, type the due date from the table above (the Due Date field starts empty), give the invoice the next number in your series and replace the sample text in the Terms & Conditions box with your own terms.

The generator is free and unmetered for normal use; an anti-abuse cap of 20 PDFs per device per day (200 per IP) applies, well above ordinary use, and blank template file downloads are not metered. A one-line "Created free with myinvoicetemplate.com" credit is switched on by default and one free checkbox in the settings turns it off. Your draft is stored in your own browser on this device, so download and keep the PDF you need.

Related tools: the invoice due date calculator for a single invoice (including end-of-month terms) and the invoice number generator for numbering each invoice.