How to Invoice a Client: A Step-by-Step Guide
The Issueable Team
Small business operations
Invoicing a client isn't complicated, but small mistakes cost you days of float and the occasional bad debt. Here's the short, practical version — what to put on the invoice, when to send it, and how to chase a late payer without burning the relationship.
Why the mechanics of invoicing matter
Most late payments aren't disputes — they're friction. The invoice arrived as a Word attachment with no due date, or the buyer's AP system rejected it because the PO number was missing, or it was addressed to the wrong cost center. Fixing the invoice itself is the cheapest cash-flow improvement most small businesses can make.
This guide is the minimum viable version: what a professional invoice includes, when to send it, and how to handle the awkward second and third follow-ups.
What to include on a client invoice
A complete invoice has seven blocks. Missing any one of them slows payment, sometimes materially.
- Your business info. Legal name, address, email, and phone. If you're incorporated, use the legal entity name exactly as it appears on the buyer's master vendor list — mismatches trigger AP reviews.
- Client info. The bill-to name, address, and (where possible) a named AP contact. "Accounts Payable" gets routed; "Jamie Rivera, Facilities AP" does not.
- A unique invoice number. Sequential is fine (INV-0001, INV-0002…). Don't recycle numbers across years.
- Issue date and due date. "Net 30" is industry-standard for most B2B work; shorter terms signal either a new relationship or a known slow payer.
- A clear line-item table. Description, quantity, rate, and line total. One row per deliverable. Vague descriptions ("services rendered") are the second-most-common reason invoices get held in AP review.
- Subtotal, discount, tax, and grand total. Applied in that order. If you're collecting sales tax, show the rate and amount explicitly.
- Payment instructions. Bank details, a pay link, or a note that your Stripe/Square/ACH link is in the body of the email. If the buyer has to ask how to pay, you've already lost a day.
Optional but high-leverage: a short thank-you line, your logo, and terms ("late fees of 1.5% per month begin at day 31" — more on that below).
When to send the invoice
The fastest way to get paid in 30 days is to invoice on day zero, not day seven. A few rules that hold up across industries:
- For project work, send the invoice the moment you deliver the final asset — same day, ideally within the same email thread. The buyer is still in the "I owe this person money" headspace; don't wait for the Monday admin block.
- For retainers, send on the first of the period, not the last. You're paid for the month ahead, not the month behind.
- For trades and contracting, invoice at the milestones you quoted. If your estimate said "50% on deposit, 50% on completion," stick to it — changing the cadence after the fact feels like a renegotiation.
- For e-commerce and one-off sales, the receipt acts as the invoice. Send it automatically on payment and move on.
Payment terms, in plain English
The four terms you'll see most often:
- Due on receipt. Pay now. Common for small one-off jobs and new clients.
- Net 15. Pay within 15 days. Tighter than standard; use it when you need the cash or the client has a history of slow payment.
- Net 30. Pay within 30 days. The default for most B2B work.
- Net 60 / Net 90. Pay within 60 or 90 days. Common with enterprise AP, sometimes non-negotiable. If you're offered these terms, consider pricing in the cost of the float.
Late fees are legal in most jurisdictions if they're on the invoice at the time of issue, not bolted on later. A common clause: "Invoices unpaid after 30 days accrue a 1.5% monthly late fee." Most buyers won't pay it — but naming the fee upfront is what gets the invoice off the bottom of the AP pile.
Following up on late payments
A large share of small-business invoices get paid late — by most industry surveys, somewhere around a third. The follow-up sequence that works best is predictable, friendly, and escalates slowly:
- Day 31: the nudge. Short, warm, attaches a fresh PDF. "Hi Jamie — just flagging that invoice INV-0042 is showing as unpaid on our side. Attaching in case it got lost. Happy to resend to a different address."
- Day 38: the second nudge. Still friendly; this time ask a question. "Wanted to check whether this needs a PO number or an updated entity name on our end — anything that'd help it clear AP?"
- Day 45: the structured ask. Move from friendly to direct. "Could you let me know the payment date we can plan around? Happy to jump on a quick call if it's easier."
- Day 60+: the decision. Decide whether the relationship is worth more than the invoice. For most small businesses, at 60 days you're choosing between a payment plan, a collections agency, or writing it off.
Two things to avoid: don't chase daily (it teaches the buyer to ignore you), and don't lead with late fees in the first nudge (it raises the temperature before you need to).
Common invoicing mistakes that slow payment
- Sending as a Word doc. Buyers print PDFs; Word files get held for reformatting. Always send PDF.
- Missing PO number. If your buyer's system requires a PO, the invoice will bounce to a queue you'll never see. Ask once, at the start of the engagement.
- Vague line items. "Consulting" is worse than "Kickoff workshop, May 14, 4 hours." Specifics survive AP.
- No due date. "Payable upon receipt" is ambiguous. Pick a concrete date.
- Different payee name than your contract. AP matches these. Mismatch = held invoice.
A 5-minute invoice checklist
Before you hit send, confirm:
- Invoice number is sequential and unique
- Client bill-to name matches how they appear on your contract
- Issue date and due date are both filled in
- Each line item has a clear, specific description
- Subtotal, tax (if applicable), and total are all correct
- Payment instructions or a pay link are visible
- If the buyer requires one, the PO number is on the invoice
- The file is a PDF, not a Word doc
That's the whole job. Most of the value of a good invoice comes from doing the boring fields right the first time.
Ready to invoice?
Issueable's invoice generator covers all seven blocks above, renders a clean PDF in about 60 seconds, and — if you've already sent a quote — carries the client details and line items over so you're not retyping. Start an invoice.
Frequently asked questions
- What information should always be on a client invoice?
- A complete invoice includes your business info (legal entity name, address, email, phone), the client's bill-to details, a unique invoice number, the issue date and due date, a clear line-item table with description, quantity, rate, and line total, the subtotal, discount, tax, and grand total, and payment instructions or a pay link. Missing any one of these slows payment.
- What does Net 30 mean on an invoice?
- Net 30 means payment is due within 30 calendar days of the invoice date. It's the default term in most US and Canadian B2B work. Net 15 is a shorter window, usually for smaller or newer relationships; Net 60 and Net 90 are common in enterprise AP and should be priced into your rates because you're effectively extending a line of credit.
- Can I legally charge late fees on an invoice?
- In most US states and Canadian provinces, yes — provided the late-fee clause appears on the invoice (or in a signed contract) at the time the invoice is issued, not retroactively. A common clause is 1.5% per month on the unpaid balance, which works out to roughly 18% annualized. Some jurisdictions cap the rate; check local law for enforceability and check whether your buyer is a government entity, which usually has its own rules.
- When should I send the invoice after finishing the work?
- Same day the work is delivered, ideally inside the delivery email thread. The buyer is still in a 'this was just completed' headspace, which dramatically shortens time-to-payment. For retainers, invoice on the first of the period; for milestone contracts, invoice at each milestone you quoted; for e-commerce, the receipt itself is the invoice.
- What's the best way to follow up on a late invoice?
- Run a three-step sequence: a friendly nudge at day 31 that re-attaches the PDF, a second nudge at day 38 that asks if anything on your end is blocking AP (PO number, vendor form, entity name), and a direct ask at day 45 for a specific payment date. After day 60 the conversation should shift to a payment plan, collections, or writing off the invoice. Never chase daily — it teaches the buyer to ignore you.
- Should I send an invoice as a PDF or a Word doc?
- Always PDF. Word documents get held for reformatting, rejected by buyer AP portals, and look unprofessional on mobile. A PDF renders identically on every device and archives cleanly in the buyer's accounting system. Issueable generates a clean, print-ready PDF in about 60 seconds with no software to install.