Invoice & Customer Numbering

Overview

Numbering settings control how your invoices and customers are numbered. Proper numbering is required for legal compliance and accounting accuracy.

Accessing Numbering Settings

1. Go to Business Settings > Numbering
2. Configure separate settings for Invoices and Customers

Changes are saved automatically as you type.

Invoice Numbering

Components of Invoice Numbers

Every invoice number is composed of three parts:

• Prefix (optional) — Text before the sequential number
• Sequential Number — The auto-incrementing counter
• Suffix (optional) — Text after the sequential number

Configuration Options

Prefix

• Optional text that starts every invoice number
• Supports dynamic placeholders (see below)
• Common examples: "INV-", "RG-", "RG-{YYYY}-"
• Leave blank for numbers only

Suffix

• Optional text appended after the sequential number
• Also supports dynamic placeholders
• Common examples: "-{YYYY}", "-DE"
• Leave blank for no suffix

Padding

• Number of digits in the sequential counter, padded with leading zeros
• Range: 0 to 10
• Examples:
  • Padding 3: "001", "002", "003"
  • Padding 4: "0001", "0002", "0099"
  • Padding 5: "00001", "00002", "00999"
• Recommended: 4--5 digits for most businesses

Counter Position

• The current counter position is displayed below the live preview
• docs101 auto-increments this after each invoice
• You can manually adjust the counter via the "Edit" link, but this should only be done when migrating from another system

warning

Manually changing the invoice counter can create gaps in your numbering sequence. Gaps in invoice numbers may raise questions during tax audits. Only adjust the counter if you are migrating from another invoicing system and need to continue an existing sequence.

Reset Frequency

• How often the sequential counter resets back to 1:
  • None — Numbers continue incrementing indefinitely (1, 2, 3, ...)
  • Daily — Resets at the start of each day
  • Monthly — Resets on the first day of each month
  • Yearly — Resets on January 1st of each year
• Most common: Yearly (matches the calendar year in European practice)

Dynamic Placeholders

You can use the following placeholders in the Prefix and Suffix fields. They are automatically replaced with the current date values when an invoice is created:

Placeholder	Description	Example
{YYYY}	Four-digit year	2026
{YY}	Two-digit year	26
{MM}	Two-digit month	03
{DD}	Two-digit day	15

tip

Using placeholders like {YYYY} or {YY} in your prefix or suffix means the year updates automatically. You do not need to manually change the prefix each January.

Live Preview

As you configure the numbering settings, a live preview updates automatically below the form fields. This shows you exactly how the next invoice number will look based on your current settings.

Examples

Example 1: German Company with Yearly Reset and Year Placeholder

Prefix: "RG-{YYYY}-"
Padding: 4
Reset Frequency: Yearly
Suffix: (blank)

Results: "RG-2026-0001", "RG-2026-0002", ... and on January 1, 2027: "RG-2027-0001"

Example 2: Monthly Reset with Month Placeholder

Prefix: "INV-{YYYY}{MM}-"
Padding: 3
Reset Frequency: Monthly
Suffix: (blank)

Results: "INV-202603-001", "INV-202603-002", ... and in April: "INV-202604-001"

Example 3: Simple Sequential Numbering

Prefix: (blank)
Padding: 5
Reset Frequency: None
Suffix: (blank)

Results: "00001", "00002", "00003", ...

Example 4: Short Year in Prefix

Prefix: "INV-{YY}-"
Padding: 4
Reset Frequency: Yearly
Suffix: (blank)

Results: "INV-26-0001", "INV-26-0002", ...

Example 5: Year in Suffix

Prefix: "INV-"
Padding: 4
Reset Frequency: Yearly
Suffix: "-{YYYY}"

Results: "INV-0001-2026", "INV-0002-2026", ...

Customer Numbering

Customer numbering works similarly to invoice numbering but with one key difference: customer numbers cannot be reset. They always increment sequentially.

Configuration Options:

• Prefix — e.g., "CUST-", "K-" (supports the same placeholders)
• Padding — Number of digits (0--10)
• Counter Position — The current counter, adjustable via the "Edit" link
• Suffix — Optional text after the number

docs101 automatically assigns a customer number when you create a new customer.

info

Unlike invoice numbering, customer numbering does not have a reset frequency option. Customer numbers always increment without resetting.

Legal Requirements

The requirement for sequential, unique invoice numbers is rooted in the EU VAT Directive (2006/112/EC, Article 226), so the core principles apply across all EU member states. However, individual countries have their own specific rules — especially around how to handle errors and cancellations.

Germany

• Invoice numbers must be sequential and unique (§ 14 Abs. 4 Nr. 4 UStG)
• Numbers can consist of one or more sequences of digits and letters
• Resetting the counter at the start of each calendar year is allowed and common practice (e.g., RG-2025-0001, RG-2026-0001) — the year prefix ensures uniqueness
• "Sequential" means unique and traceable, not necessarily gapless. German courts (FG Köln, BFH) have confirmed there is no legal requirement for completely gapless numbering. However, unexplained gaps can raise questions during tax audits and may lead to additional scrutiny. Best practice is to avoid gaps wherever possible
• If an invoice contains an error, you must not simply delete it. Instead, issue a cancellation invoice (Stornorechnung) that references the original number. The original invoice number stays in the system — only its value is reversed

France

• Sequential and unique numbering is strictly required (Code général des impôts)
• France is particularly strict due to the Anti-VAT-Fraud Law (Loi Anti-Fraude TVA): invoicing software must not allow invoices to be deleted or numbering gaps to be created
• If an invoice is incorrect, it must not be deleted. You must issue a credit note (Avoir) to neutralize the original invoice. The numbering sequence must remain complete and unbroken at all times

Other EU Countries

• The same core principles — sequential and unique — apply EU-wide based on the VAT Directive
• Yearly reset is common and accepted practice across the EU, as long as a prefix (such as the year) ensures uniqueness
• Some countries like Italy, Poland, or Romania have introduced their own e-invoicing platforms where invoices must be validated by the tax authority before they are considered valid
• Consult your local tax authority or accountant for country-specific rules

Best Practices

1. Plan Your Format — Decide your numbering format before creating invoices (changing later affects only future invoices)
2. Use Yearly Reset — In Europe, resetting each year matches calendar requirements
3. Use Placeholders — Use {YYYY} or {YY} in your prefix or suffix so the year updates automatically
4. Start from 1 — Begin with "001" or "0001" for a clean start
5. Avoid Gaps — Do not skip numbers; gaps raise compliance questions
6. Document Your Format — Write down your format for your accountant's reference

Changing Numbering Scheme

You can change the numbering scheme at any time:

1. Go to Business Settings > Numbering
2. Update the settings (prefix, suffix, padding, reset frequency)
3. Changes are saved automatically

info

Only future invoices use the new format. Existing invoices keep their original numbers.

Migration from Other Systems

If you are migrating from another invoicing tool:

1. Note your last invoice number — e.g., "RG-2025-0500"
2. Set the counter accordingly — Click "Edit" next to the counter position and enter the next number (e.g., "501")
3. Match your old numbering format — Use the same prefix, suffix, and padding
4. Keep old system data — Maintain backups of invoices from your previous system

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Next: Configure Email Settings for invoice delivery.