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An invoice is quickly written – it is correctly written when every mandatory detail per § 14 UStG is in, the number is gapless and you can present it unchanged for eight years. Here is what matters.
The mandatory details are in § 14 (4) of the German VAT Act (UStG). If one is missing, your customer cannot deduct input tax – and sends the invoice back.
Not the looks but these points cost time with customer, accountant and audit:
Invoice numbers must be unique and sequential. Parallel spreadsheets or deleted drafts create gaps that have to be explained in an audit.
Without a date or period of performance the invoice is incomplete. For ongoing projects and retainers the billed period belongs on every invoice.
A sent invoice is not overwritten but cancelled or corrected with a credit note – referencing the original. Otherwise GoBD immutability is violated.
Billed hours without tracked time or a signed timesheet cannot be proven in a dispute.
The invoice is created from quote, project or tracked time – with every mandatory detail from your master data.
Customer, tax number, number sequence, tax rates and period of performance come from the system. When sending you pick PDF, XRechnung or ZUGFeRD.
Booked invoices stay as they are. Corrections run as cancellation or credit note linked to the original, every PDF as PDF/A.
Hours from time tracking, line items from the quote, milestones from the project – without double billing.
Invoices are accounting records and must be retained for eight years (§ 147 (3) AO); the period starts at the end of the calendar year in which the invoice was created. During that time it must remain unchanged and readable – as PDF/A in the archive, not as an editable file in a folder. What the GoBD require in detail is on our GoBD page.
Invoices hang on quotes, projects and time – continue here.
Between businesses only for a transitional period: since 2025 a PDF counts as an "other invoice", and the obligation to issue e-invoices phases in from 2027. What applies when is on our e-invoicing page.
It has to be unique and sequential. One sequence per organisation, location or brand is allowed – gaps in it should be explainable. In cashwerk the sequence assigns the number only on booking; drafts create no gaps.
As the date or period in which you performed – for projects and retainers the billed month or phase. cashwerk takes the period from tracked time or the milestone.
Do not overwrite it. Cancel a sent invoice with a cancellation invoice or correct it with a credit note – both reference the original. That keeps the thread traceable.
Yes. Partial and progress invoices belong to a chain; the final invoice deducts amounts already invoiced and deposits. cashwerk calculates the chain automatically.
Eight years (§ 147 (3) AO for accounting records), starting at the end of the calendar year in which the invoice was created. Books, inventories and annual accounts stay at ten years.
Mandatory details from master data, numbers from the sequence, line items from quote and time tracking – and the PDF/A in the archive. Invoices are unlimited on every plan.
Invoices in cashwerk