How to send a monthly invoice as a contractor
Some clients want one invoice a month instead of four or five weekly ones. Monthly invoicing means less admin, but a longer wait for your money and a bigger document to check. Here's a layout that stays readable, and how to choose the period and terms.
On this page
Weekly or monthly?
| Weekly | Monthly | |
|---|---|---|
| Cash flow | Steady, predictable | Lumpy, longer wait |
| Admin | 4–5 invoices a month | 1 invoice |
| Checking | Easy: 7 rows | Longer: up to 31 rows |
| Typical clients | Agencies, site contractors | Direct clients, consultancies, retainers |
Use whatever the client's accounts team works to, but if you can choose and cash flow matters, weekly usually wins.
Choosing the billing period
The cleanest approach is to bill complete calendar months (1st to the last day) and send the invoice in the first few days of the following month. For example, an invoice issued on 12 October 2026 covers 1–30 September 2026. Show the period prominently: "Period: 01/09/2026 – 30/09/2026". Some clients use their own four-weekly periods instead. If so, match their dates exactly, as they'll be reconciling against their own timesheets.
A layout that stays readable
- One row per worked day: day and date, location or project, rate, hours, overtime hours, amount.
- Hide non-working days. Weekends and days off with no hours just add clutter. Twenty rows fit comfortably on one A4 page.
- Show the day rate once in the header (e.g. "Day rate: £165.00 (8h)") rather than repeating it.
- Totals at the end: total days, total hours, total overtime hours, and the amount.
- If it runs to a second page, repeat the column headings and keep the totals on the last page.
Example (extract)
| Day & date | Location | Hours | OT | Amount |
|---|---|---|---|---|
| Tue 01/09 | Site A | 8 | 0 | £165.00 |
| Wed 02/09 | Site A | 8 | 2 | £216.56 |
| Thu 03/09 | Site A | 8 | 0 | £165.00 |
| … | ||||
| 22 days · 176 h · 6 h OT | £3,784.68 | |||
Here, 22 days at £165 is £3,630. Overtime at ×1.25 is £25.78125 an hour, and the 6 overtime hours are three days with 2 hours each. Each of those days is £165 + £51.5625 = £216.5625, which rounds to £216.56. The total is 19 × £165 + 3 × £216.56 = £3,784.68. Always add up the rounded lines, so the total matches the rows exactly.
Payment terms for monthly invoices
14 or 30 days from the invoice date is normal. Put the actual date on the invoice ("Payment due by 11/11/2026"). If you haven't agreed terms with a business client, the statutory default is 30 days after they receive the invoice. See invoice due dates explained.
Common mistakes
- Overlapping or missing days between one month's invoice and the next.
- Including bank holidays you didn't work.
- A single "September labour – £3,784" line that the client can't check.
- Rounding the hourly rate before multiplying, which causes a drift of a few pence over a month. See our day rate guide.
Worked example: the same month with CIS
If you work under CIS, the monthly invoice needs a summary at the foot. Taking the September example above, where the labour total is £3,784.68 and none of it is materials, a 20% deduction is £756.94 (£3,784.68 × 0.20 = £756.936, rounded to the penny). The amount paid to you is £3,784.68 − £756.94 = £3,027.74. If you also bought materials for the job, show them on separate lines and the deduction is taken from the labour only. See the CIS invoice guide and the CIS calculator.
What monthly billing does to your cash flow
The wait is longer than most people expect. Suppose you work 1 September to 30 September, issue the invoice on 1 October and have 30-day terms. The money is due on 31 October. The first day you worked was paid for 60 days later, and the last day 31 days later. With weekly invoices and a Friday due date, the same first day would be paid within about a week. If a client only accepts monthly invoices, ask for shorter terms, such as 14 days, or agree a mid-month payment on account. The due dates guide explains how to word them.
Check before you send
- The period starts the day after the last invoice ended, with no gap and no overlap.
- Each worked day appears once, and days off are not shown.
- Overtime hours match the timesheet your client approved.
- The day count and total hours at the foot agree with the rows.
- The due date is a real date, not just "net 30".
- Invoice number follows on from your last one. See invoice numbering rules.
To check the overtime arithmetic, use the overtime calculator. If a month goes unpaid, the late payment interest calculator shows what you can add on a business invoice.
Not sure which cycle suits you? See weekly vs monthly invoicing for tradesmen.
Frequently asked questions
Which period should a monthly invoice cover?
Usually the previous complete calendar month, unless your client works to its own period dates.
Should I list every day of the month?
List the days you worked; hiding non-working days keeps it short and readable.
What payment terms suit monthly invoices?
14 or 30 days are common. Always show the actual due date.
Can I switch a client from weekly to monthly invoices?
Yes, if you both agree. Finish the last weekly invoice at a clean date, such as a month end, then start the monthly period the day after so no days overlap or go missing.
Does CIS change a monthly invoice?
The layout is the same, but you add a summary showing labour, materials, the deduction and the amount payable. Show materials on their own lines so the deduction is taken from labour only.
Sources
This guide is general information, not legal, tax or financial advice. Rules and rates change, so check the linked GOV.UK pages for the current position.