Guides for small businesses

The rules behind your invoices – explained clearly.

Which details are mandatory, which deadline runs when and what changes with e-invoicing: these pages explain the requirements along a concrete process. They don’t replace a tax advisor, but they help you ask the right questions.

Writing documents

Writing an invoice →

Structure, mandatory details and the process from the work itself to sending.

Writing an estimate →

How an inquiry becomes an estimate that still matches the invoice later.

Mandatory details for small businesses →

What a Kleinunternehmer invoice has to include – and what it doesn’t.

Details and numbers

Invoice number →

Rules, structure and number sequences that still add up years later.

Tax number on the invoice →

Tax number (Steuernummer) or VAT ID – which one fits when.

Small business rule (Kleinunternehmerregelung) →

What the rule means for your invoices and when it ends.

E-invoicing

E-invoicing mandate →

Who has to receive and issue e-invoices from when – and what applies during the transition.

After sending

Invoice deadlines →

Payment terms, limitation period and retention are three different deadlines.

Writing a dunning letter →

Process, deadlines and a tone that doesn’t damage the client relationship.

GoBD and invoices →

What a traceable, unalterable process actually has to do under the German rules for proper digital bookkeeping.

Winning clients

Client acquisition →

Positioning, channels, follow-up and referrals as a repeatable system.

Winning clients with Meta ads →

Instagram and Facebook ads that aim at paid jobs instead of reach.

Building a website with AI →

Your own site in hours – and one that brings in inquiries.

DIY SEO →

Our complete approach with AI and live data, laid open – build in public.

Facts & figures

Businesses and the self-employed in numbers →

Businesses, self-employed people, start-ups, insolvencies and payment behavior – with year and source.

The next step

Knowing the rules helps. A process that follows them helps more.

Sumaro keeps mandatory details, number sequences and deadlines inside each transaction instead of leaving them to you.

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