What an invoice must contain
The elements that make an invoice a valid business document almost everywhere, plus what actually keeps you waiting for the money.
Guides
Written for the person who does their own paperwork and would rather not learn tax law to do it. Each one answers a question that comes up the first time you bill a client abroad, count somebody’s overtime, or send a claim to a finance team you have never met.
EU reverse charge
When you charge 0% and write “reverse charge” instead of adding VAT, what must appear on the invoice, and the one number to verify first.
UK VAT invoices
The required fields for a VAT-registered business in the UK, when a simplified invoice is allowed, and how sales to the EU are treated now.
Invoicing US clients
Why there is no VAT line, which tax form they will ask you for, and how to stop intermediary banks eating the total.
Korea: 세금계산서 vs invoice
A commercial invoice and a Korean tax invoice are different documents issued through different systems. Mixing them up is the mistake to avoid.
Invoice numbering
A scheme that stays sequential, sorts correctly, survives a year boundary, and does not advertise how few invoices you have sent.
Payment terms and late fees
What Net 30 means precisely, the statutory interest you may be entitled to in the UK and EU, and the wording that makes terms stick.
Billing in another currency
Who carries the exchange risk, what to write when your books are in one currency and the invoice in another, and how to stop bank fees eating the total.
Proforma vs commercial invoice
Four documents that look alike and do different jobs. Sending the wrong one is how a shipment sits at customs.
Getting paid on time
What to do on day 0, day 3, the due date and thirty days after — and why the first email should go before the invoice is late.
How overtime is counted
The two thresholds, why they are not added together, what happens to unpaid breaks, and the rounding rule that quietly costs people money.
Billing by the hour
How to set a rate, what to do about small tasks, when to move to a retainer, and why the timesheet should reach the client before the invoice does.
Expense claims that get approved
Per-category totals, mileage shown as working, what to do about a foreign receipt, and the policy questions worth settling before anyone spends anything.
Purchase order vs invoice
What a PO is, why larger clients insist on one, what the three-way match is, and why a freelancer should ask for a PO number before starting.
How a repayment splits
Why early payments are mostly interest, what the total interest figure tells you, how extra payments shorten a loan, and why your lender quotes a different number.
Then make the document
The tools print the wording these guides describe — reverse-charge notes, tax labels, bank-charge instructions, mileage shown as distance times rate — without you having to remember any of it.