The timesheet and pay-and-bill system behind your weekly pay run

Monday's timesheets become the week's pay and the week's invoices.

A typical business running one of these has 20 to 100 internal staff across one to four branches, between 300 and 2,000 temporary workers on assignment in any week in industrial, driving, warehouse, care or office roles, and a payroll team of two to five running a weekly pay run and weekly client invoicing.

Almost every agency this size runs a bought candidate and client database. This page is about the system beside it, the one the agency had built for itself, which takes over once a temp is placed. Written in 2009 or in 2020, it runs the same week.

In the payroll team's words, it holds each assignment with its pay rate and charge rate, takes in the timesheets however they come (paper, emailed spreadsheets, a client portal's export, the temps' app), gets each one authorised by the client, and applies the overtime, night and weekend rates from that client's contract. It pays PAYE temps, umbrella companies and limited company contractors, invoices each client with the timesheet behind every line, tracks holiday pay and each worker's weeks in the same role under the Agency Workers Regulations, and reports margin by client.

The rules it applies belong to the agency:

• A pay rate never changes without its charge rate.
• Nobody is paid without a client-authorised timesheet, except at the named clients who authorise the week by email.
• A worker reaching 12 weeks in the same role with the same hirer moves to the comparable rate the client has confirmed, with the count following the regulations' rules on breaks.
• Holiday pay is rolled up at 12.07% only for workers classed as irregular hours or part-year; everyone else accrues it and is paid when they take leave.
• Pay below the legal minimum for the worker's age stops the pay run.

The first version arrived somewhere between 2005 and 2013, when the agency paid a contractor to write it a Windows pay-and-bill program on the .NET Framework. The data is in SQL Server, the payslips, remittances and client invoices come out of Crystal Reports, and the clients' timesheet spreadsheets are pulled in by an Excel import that expects its columns in a fixed order. It lives on the server in the head office and is installed on the payroll team's desks.

The contractor stopped taking calls years ago, and the only changes since are the ones payroll could make in a settings table. A branch manager who wants to see a timesheet phones head office. Each year's new minimum wage rates go in by hand, and nobody is sure which other tables should have changed with them.

Between 2016 and 2022 other agencies had the same system built for the browser, around the two things the old program never had: a timesheet portal for clients and an app for the temps. A small agency or a freelancer wrote it in PHP or React, Angular or Node, with the app in React Native, or someone in operations put it together in Power Apps or Bubble. From the payroll desk it looks like the future: hours entered on a phone, approved from a link, each client seeing its own week.

Client authorisation is what stranded it. The portal worked for the clients willing to log in; the rest still email spreadsheets, keyed on Monday by the payroll team the portal was meant to spare. When rolled-up holiday pay was allowed for irregular hours and part-year workers in 2024, the change was patched into the pay screen and never reached the invoice template, so some clients are still charged the old way and the margin report cannot say by how much. The freelancer behind the rate logic has moved on. Since 2023 a few agencies have tried the timesheet side again in an AI app builder, and those attempts tend to stop at the first client whose overtime rule does not fit the form.

Up to two thousand people paid each week by a payroll team of a few, with every paid hour billed to the client who authorised it.

The pairing of pay and charge is what the agency lives on. Every assignment carries both rates, and every authorised timesheet produces a pay line and an invoice line together, so an hour cannot be paid and left off the invoice. The margin on each client is known the week it is earned.

A pay line under the minimum never leaves the building, the 12-week count brings in the comparable rate on the week it is due, and holiday pay follows each worker's classification instead of whoever happened to key the timesheet.

When a client queries a line, payroll opens the timesheet and the authorisation behind it, and the query usually ends there. Every client's overtime arrangement and every exception agreed over the years is already in it, which is why the agency still runs the week on it.

The pressure on systems like this mostly comes from outside the payroll office.

Umbrella pay is now the agency's to answer for. From 6 April 2026 the recruitment agency supplying a worker through an umbrella company is responsible for PAYE on that worker, and jointly and severally liable if the umbrella fails to pay. Whichever generation built it, the system records the payment to the umbrella and nothing about what the umbrella then paid, so any checking happens in a spreadsheet beside it.

The client's decision on a contractor has nowhere to go. Since April 2021, medium and large private sector clients have decided whether each limited company contractor falls inside the off-payroll working rules. The assignment screen knows the contractor is a limited company and nothing more, so the decisions sit in an email folder.

The server and the database both have dates. Where the program runs on Windows Server 2016 over a SQL Server 2016 database, the database lost its updates in July 2026 and the server loses its own in January 2027. Moving a payroll database needs a week with no pay run in it, and an agency that pays weekly never has one.

A new client means a new spreadsheet layout. Each client's timesheet export has its own columns, and the import only knows the layouts the agency had when it was written. A new client's sheet gets retyped, or reshaped by hand into an old client's layout, every week.

The same rates and rules, open at every branch, with the umbrella and contractor records the agency now has to keep.

Every client's timesheet in, whatever the layout. Each client's spreadsheet layout is mapped once and kept in settings, so a new client or a moved column stops meaning weeks of retyping. The portal, the weekly authorisation email and the temps' app all land on the same assignment.

A record behind every umbrella payment. What each umbrella received, what it reported paying the worker and HMRC, and which umbrellas have not sent their figures, held on the assignment beside the payment.

The client's decision on each contractor. The off-payroll decision on the assignment with its date and document, and a contractor placed inside the rules held back from being paid without PAYE.

Invoices that follow the pay rules. Holiday pay, the 12-week comparable rate and the overtime multipliers set once for both sides, so a change to pay reaches the invoice that week and the margin report can be trusted.

Pay and bill from any branch. The same screens in a browser at every branch and from home, one login each, so a branch manager looks up a timesheet instead of phoning head office.

Off the 2016 servers. The database on a version that still receives updates, on a server that does too, with a backup restored to prove it.

The rules where payroll can read them. The authorisation exceptions, the minimum wage check and each client's multipliers out of the code and into settings, written down with the people who apply them.

The old program keeps paying people while each piece goes in beside it, and nothing is switched off until its replacement has matched a pay run.

The keying on Monday, the checking before the pay run goes, and the questions no report was written to answer.

Timesheets read onto their assignments. A photographed paper sheet, a PDF from a site supervisor, a client's spreadsheet in an unmapped layout: AI reads each one, matches names and dates to live assignments and drafts the hours, marking what it could not read, for payroll to approve. When a third of 300 to 2,000 weekly timesheets arrive like that, about 100 to 670, keying them at a minute and a half each comes to anything from a morning to about two days' typing a week, and checking the drafts hands most of it back.

The pay run checked before it goes. AI reads every pay line against its assignment and the worker's recent weeks and lists the ones that look wrong: hours over a limit, a charge rate below the pay rate, one worker paid twice across two branches, a week unlike any that worker has had. A person clears each flag. Reading 300 to 2,000 pay lines by eye at ten seconds a line works out at between about an hour and five and a half hours; fifteen or so flags at two minutes each take half an hour to clear.

Questions asked of the assignments. Which workers reach week 12 with their hirer next month? Which clients have timesheets still unauthorised after a week? AI answers from the assignment and timesheet records and lists every record it counted, so the branch manager checks names rather than trusting a total. Setting one report against another by hand for 500 live assignments, at half a minute a line, adds up to about four hours, the afternoon a month those answers replace.

Not worth doing: AI deciding whether a contractor falls inside the off-payroll rules, or choosing which temp gets a shift. The first is the client's decision to make and to explain; the second is a consultant's judgement of people, and a model could not say why it chose.

Each of these reads or writes the records the pay run depends on, so none goes live before those records can be changed on a copy. The assessment maps where AI would pay back soonest on the agency's own pay week.

Safe to change first, then the records the law now asks for, then the timesheets, with the old program paying people until each new piece matches it.

1. Stabilise. The source code found and matched to the running program, or the portal's code and hosting recovered, the database on a version still receiving updates, a backup restored, and a test copy where a past pay run can be repeated. This goes first because nothing that pays people is changed without a copy to try it on, and because Windows Server 2016 support ends in January 2027.
2. Umbrella and contractor records. The umbrella payment record and the client's off-payroll decision beside the pay run, on the existing database, with the pay run unchanged. The liability has been live since April 2026.
3. Timesheets from every client. The spreadsheet layouts mapped, portal and email authorisation landing in one place, and the temps' app released again.
4. Pay-and-bill screens in a browser, invoices from the same rules, the margin report. Each priced before it starts, and run beside the old pay run until the totals agree.
5. Retire the old program once nothing leans on it. Expect the payslip to go last, because the temps know what theirs looks like.

The assessment is from £395 + VAT, sized on a free one-hour consultation, with an exact price before you commit. For a pay-and-bill system that means a few days with the payroll team, a branch manager and the code, following each rate from the assignment to the payslip and the invoice, and a report with costed options and a fixed price for each. Each stage after that is priced before you commit to it. How we work, what drives the price and the payment terms each have a page.