Measure your own delay before blaming the customer
Split the wait into two numbers. Days to invoice: work finished to invoice issued. Days sales outstanding: invoice issued to money received. Almost every company watches the second and has never measured the first.
When companies do measure it, the result is usually uncomfortable. Weeks disappear between a technician finishing and an invoice leaving, and no customer is responsible for a single day of that. It is also the easier half to fix, because it is entirely within your control.
Invoice from the record, not from memory
The reason invoicing lags is that somebody has to reconstruct what happened: what was done, what parts went in, whether the extra two hours were agreed. That reconstruction is slow, error-prone and frequently postponed.
If the completion record already contains the work, the readings and the parts, the invoice is a transformation rather than an investigation. Companies that make this change typically go from weeks to the same day, without anybody working harder.
Make it easy to pay you
A surprising amount of late payment is friction. The invoice does not say how to pay. The bank details are in an email from two years ago. The reference is unclear so the payment arrives unmatched and sits.
Put your payment instructions on every invoice: how to pay, where, and what reference to quote. Where cards or online payment are not available, say plainly what is, rather than leaving the customer to work it out. The clearer the instruction, the fewer days it takes.
Chase on a schedule, politely, early
Most chasing is emotional: nothing for six weeks, then an irritated phone call. A schedule works better and costs less goodwill. A courteous reminder a few days before due, one on the due date, one a week after, then a call.
Early contact also surfaces the real reasons, which are frequently not reluctance: the invoice went to the wrong person, a purchase order number is missing, or a query nobody passed on. Each of those is solvable in minutes and otherwise adds a month.
Know who actually pays
In commercial work the person who called you is rarely the person who pays you. The invoice has to reach the right address, carry the reference their system requires, and often quote a purchase order raised before the work began.
A missing purchase order number is one of the most common causes of a silently unpaid invoice, because the customer's system rejects it without anybody telling you. Capture the billing contact and any reference requirement when the job is accepted rather than discovering it six weeks later.
Deal with disputes immediately, not eventually
A queried invoice that sits for three weeks while somebody works out who should answer it becomes a queried invoice that is forty days overdue. The query itself is usually small: a line the customer does not recognise, a variation they do not remember agreeing, an amount that differs from what they were told on site.
All three are answerable in minutes if the job record is good. What was done, what was agreed, who signed. Companies that can answer the same day resolve most queries without a concession; companies that take a fortnight frequently end up discounting simply to close it, because by then the argument has become about the delay as much as the money.
Terms, deposits and staged payments
For larger installation work, payment staged against milestones protects cash flow and limits exposure if a project stalls. A deposit for equipment is standard practice in most markets and entirely reasonable to ask for.
Agree terms before the work, in the quotation, where they are a condition rather than a demand. Terms introduced on an invoice are not terms, they are a request, and they are treated accordingly.