How to write an invoice: a clear guide for the self-employed
An invoice doesn’t have to be pretty. It has to be right: the correct recipient, a traceable service, complete mandatory details, clean amounts and deadlines. This guide follows the steps in the order you take them – and shows where the most common mistakes sit.
1. Check the parties and master data
Start with the full name and address of both you and your client. For companies, the correct legal name matters more than a familiar short name. Also check whether the invoice recipient differs from the person who placed the order. A clean master data record prevents follow-up questions and later corrections.
Your tax identification and bank details should be maintained in one central place. Changes belong in a controlled setting, not in a single invoice copy. That keeps later invoices consistent without old documents being overwritten unnoticed.
2. Describe the service and period clearly
A line item should show what you delivered. Generic wording like “services” does little for the client or the bookkeeping. Describe the project, period, scope or result so that an outsider can follow the context.
For ongoing services, the service period and the agreed payment term belong visibly on the document. Hours, flat fees and individual items can be presented differently, but they have to add up arithmetically to the total.
- Name the service specifically
- Add the period or delivery date
- Keep quantity, unit and price traceable
- Clearly label agreed flat fees
3. Check amounts and tax treatment
Check the net amount, tax amount and gross amount separately. For small business owners (Kleinunternehmer), reverse charge or other special cases, you cannot simply use the standard scheme. The note has to match the actual case and must not suggest VAT that is not owed.
Round only at the intended calculation step and check that the sum of the line items matches the stated total. A preview before sending is especially valuable when an invoice was carried over from an estimate or from recurring line items.
4. Invoice number, date and payment term
A unique invoice number helps with queries, incoming payments and your own filing. It does not have to consist only of sequential digits, but it should be assigned uniquely and traceably. Number sequences belong to the organization and should not be shared across several workspaces.
The date of issue is distinct from the date of service. A payment term should be phrased as a specific date or an understandable deadline. That way your client knows when payment is expected, and your dunning process can build on it.
5. PDF, e-invoice and filing
For many clients, a PDF is still the right way to send an invoice, but it is not automatically a structured e-invoice. If the recipient requires XRechnung or ZUGFeRD, you need the matching format and the data that goes with it. If in doubt, ask before sending instead of rebuilding a file several times.
Keep the version you sent and the relevant records so that you can find the transaction again later. Software should link invoice, estimate, payment and dunning letter without quietly changing the finalized version.
Prepare an invoice in ten minutes
A repeatable routine starts with a saved client record and a clear document template. Open the job, carry over the agreed line items and add only the details that are settled after the work is done. These usually include the date of service, invoice number, payment term and any deviations from the estimate. That doesn’t make the invoice automatically correct, but the number of transfer errors drops considerably.
Read the preview once as your client would and once as your tax advisor would. Could a stranger tell who delivered what, when and at what price? Is the amount due unambiguous? Are notes on the small business rule (Kleinunternehmerregelung), reverse charge or other special cases really appropriate? These two perspectives catch many mistakes before a message goes out.
- Use the job or estimate as your starting point
- Read the preview from the client’s and the tax perspective
- Explain deviations from the estimate visibly
Sending and filing are part of writing an invoice
A finished invoice only becomes a reliable record once sending and filing are traceable. Note when and through which channel you sent it. For a portal or an e-invoice, the technical proof of transmission is part of it; for an email, the sent message with its attachment can be relevant. The saved version must not be silently overwritten afterwards.
If an invoice comes back, don’t simply create a new number with the same content. Check whether it is a technical error, a wrong address or a correction of substance. Depending on the cause, resending, a correction or a credit note may be necessary. If in doubt, professional advice determines the right route.
Sources and context
Legal and tax rules can change. What counts are the current primary sources and your professional advice.
Put this into practice on your very next job.
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