How to Bill a Client Monthly for Services (by Days Worked)

You work for a client two or three days a week, sometimes more, sometimes less. Some days are research, some are design, one is a workshop on site. At the end of the month you need one invoice that covers all of it, and you need to remember which days were which.

Monthly billing is one of the simplest ways to get paid for ongoing work, as long as you keep track during the month instead of reconstructing it on the 31st. This guide covers how to log the days, how to turn them into an invoice, a sample with numbers, and the dates and due dates that keep payment on schedule.

When does monthly billing make sense?#

Billing once a month for the days you worked suits:

• Ongoing work with a variable number of days. Embedded design or development support, consulting a few days a month, regular editing or production days.
• Regular services on set days. Training every Tuesday, a weekly on-site day, a monthly reporting day.
• Clients with a monthly payment run. Many accounts teams process supplier invoices on a fixed cycle, so one predictable invoice a month fits their routine.

It suits less well when the client pays the same fee every month no matter how many days you work. That is a retainer, and it is billed differently: see how to bill a monthly retainer. For a single short booking, invoice when the booking ends, as covered in how to invoice a day rate.

How do you keep track of your days during the month?#

The invoice is only as accurate as your log. Pick one place to record days and update it the same day you work.

If you use a spreadsheet, keep it simple: columns for Date, Client, Service, Days (1 or 0.5) and a short Note. At month end, a formula like =SUMIFS(D:D, B:B, "Harbor", C:C, "UX research") totals the days for one service for one client.

How do you turn a month of days into an invoice?#

On the last working day of the month, or the first of the next, work through these steps.

1. Close the month

Check your log against your calendar, sent emails and any meeting invites. Add any day you missed and remove any day that slipped. It takes five minutes and prevents most disputes.

2. Total the days per service

Count the days for each service separately. If you agreed different rates for different kinds of work, they need separate totals.

3. Write one line per service

One line for each service, with the number of days, your rate and the amount. Under each line, list the dates worked. Twelve days across three services is three lines, not twelve.

4. Add the billing period

Write it near the top: "Billing period: 1 to 31 October 2026". It tells the client at a glance what the invoice covers and stops a late day from being billed twice.

5. Set the invoice date and due date

Date the invoice on or after the last day you worked in the period. Then set a due date based on your agreed terms, written as a real date.

6. Add tax if you are registered, and the total

Add VAT, GST or sales tax only if you are registered and the service is taxable where you are. Then the subtotal and the total due.

7. Include proof of the days

A list of dates on each line is often enough. If the client or an agency wants signed-off proof, timesheet invoices explains how to attach it so the invoice is approved first time.

8. Send it to the person who pays

Send it to accounts payable as well as your day-to-day contact, unless the client told you otherwise. Keep a copy with your log for your own records.

Sample monthly invoice for services#

Here is a month for a UX consultant with three services at two rates, billed at the end of October.

INVOICE                              INV-2026-010
Issue date: 31 Oct 2026      Due date: 14 Nov 2026
Billing period: 1 to 31 October 2026

From: Ana Costa UX
      10 Bridge St, Bristol BS1 2AB
To:   Harbor Clinics Ltd, Accounts Payable
      40 Mill Rd, Manchester M1 2CD

Description                Days    Rate     Amount
UX research                   5    £500     £2,500
  1, 2, 8, 9, 15 Oct
Design sprints                6    £500     £3,000
  20, 21, 22, 27, 28, 29 Oct
Workshop facilitation         1    £650       £650
  23 Oct, on site
                          Subtotal          £6,150
                          VAT       not registered
                          TOTAL DUE         £6,150

Payment: bank transfer within 14 days.
Account name: Ana Costa
Sort code: ...   Account number: ...

The client can check every figure without opening another document: 12 days, three services, dates for each, one total.

What dates should a monthly invoice show?#

A monthly invoice carries three kinds of date, and each one does a job.

• The billing period or dates worked. In the UK, gov.uk says an invoice must include the date the service was provided as well as the date of the invoice. For monthly work, the billing period and the list of dates do exactly that. The European Commission's VAT invoicing rules similarly ask for the date of the transaction when it differs from the invoice date.
• The issue date. The day you send it. The last working day of the month or the first working day of the next are both common. Avoid dating it before the last day you are billing for.
• The due date. When payment is expected, written as a date.

If you are registered for VAT, check the timing rules too. In the UK, HMRC says a VAT invoice must usually be issued within 30 days of the date you make the supply, and it must show the time of supply and the extent of the services. Billing promptly at month end keeps you well inside that.

When should a monthly invoice be due?#

Agree the terms before the first month starts, then use them every time. Common choices for monthly service invoices are 7, 14 or 30 days after the invoice date. Shorter terms mean less time waiting; longer terms may be what a large client's payment run requires.

If you never agreed a date, the default can be longer than you expect. Under UK late payment rules, a payment is late 30 days after the customer gets the invoice, or after you provide the service if that is later. Agreed payment terms between businesses should usually be no more than 60 days. For choosing and wording terms, see net 30 payment terms.

How do you bill several services in one month?#

Group the days by service, and decide how much detail the client needs.

If one day covered two services, say a morning of research and an afternoon workshop, agree how to split it: half a day on each line, or the whole day on the higher-rate service. Write the rule down once and apply it every month.

How to bill monthly in BillBee.work#

Monthly billing by days worked is what BillBee.work, a free invoice maker for freelancers, does best.

1. Add the client once. Each client (an "organisation") keeps its own currency, invoice number prefix, optional tax, and saved services with rates, such as "UX research, £500 a day" and "Workshop facilitation, £650 a day".
2. Log days on the service calendar. Open the calendar page, pick the client and the month, and mark which services ran on which days. Each service has its own colour, and a day with two services shows both. Fill weekdays and Clear speed things up, it saves automatically, and the week can start on Sunday or Monday.
3. Auto-fill the invoice. At month end, create an invoice and choose Auto-fill from a logged month. It fills in the services and their days from that client's calendar for the month you pick.
4. Print the work log. Turn on Work log in invoice to print a small calendar of the days worked on the invoice, in any of the five templates.
5. Check the due date and share. When you auto-fill from a logged month, the due date defaults to 7 days after the end of that month. Change it to your agreed terms. Then copy the share link into your email; the client opens it without an account. An unpaid invoice is marked overdue automatically once its due date passes.

A few honest limits. BillBee.work has no recurring invoices, so you create each month's invoice yourself, though auto-fill makes that quick. There is no separate notes field, so type the month into the line description, for example "UX research, October 2026". It does not send emails or reminders for you. And the free plan keeps up to 10 saved invoices, which is under a year of monthly invoices for one client; Pro removes the limit and adds PDF download.

Month-end checklist#

Run through this before you send each monthly invoice:

1. Log is complete: every day worked, with its service.
2. Days are totalled per service and match your log.
3. Each line shows days, rate and amount, with dates underneath.
4. The billing period is stated, for example 1 to 31 October 2026.
5. The issue date is on or after the last day billed.
6. The due date matches your agreed terms.
7. Tax is added only if you are registered.
8. Payment details are correct and complete.
9. It is going to accounts payable and your contact.
10. A copy is saved with your log for your records.

For the bigger picture, from setting terms to following up, the guide on how to invoice as a freelancer covers every step.

Create invoices that get you paid faster.

Day rates, hourly or fixed prices, a work log your client can check, and five clean templates. Free to start, no credit card.

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