Number series in Business Central

A number series in Business Central is the pattern that produces unique identifiers — customer numbers, sales order numbers, posted invoice numbers, item numbers, dimension codes, and dozens more. The mechanism is simple, but the design decisions inside it shape audit, statutory compliance, and integration cleanliness for the life of the system.

The model. Each number series has a code, a description, and one or more number series lines. A line defines a starting number, an ending number, an increment, an optional starting/ending date, and whether the line is currently active. When a number is requested, BC picks the relevant line based on the document date and returns the next number.

Manual vs auto-numbering. Each master record type and each document type can be configured to use a number series automatically, allow manual input, both, or default to automatic with manual fallback. The default is usually automatic with manual allowed for migration; tighten to "automatic only" after go-live to prevent ad-hoc numbering.

Number series relationships. A series can be linked to related series so users can pick from a list of related codes at the point of entry. Used heavily for documents with several flavours (e.g. domestic sales orders, export sales orders, intercompany sales orders) where each has its own number range.

Posting series. Most posting document types use two series — one for the unposted document (e.g. sales order numbers, where the order may be edited many times) and one for the posted document (e.g. posted sales invoice numbers, which are immutable). Some statutory regimes require strict sequential, gap-free posted numbering, in which case the posted number series is configured for no gaps and is highly disciplined.

Date-driven sequences. Each number series line can have a starting and ending date, so January gets one prefix and February gets another. Common for compliance regimes that require year-prefixed numbering (e.g. INV-2026-001 in 2026, INV-2027-001 in 2027). Multiple active lines with overlapping dates pick by date precedence.

Gaps and gap-handling. Posting failures can leave gaps in sequential numbers. For non-statutory series this is harmless; for statutory series, customers must investigate every gap. The Allow Gaps setting controls whether the series tolerates gaps under high concurrency.

Common pitfalls.

• Reusing a series across legal entities. Don't — each company should have its own series even if the codes look similar.
• Starting too generously. A series defined 1–9999999 looks generous until you realise audit always shows the starting boundaries; pick realistic ranges with clear year prefixes.
• Skipping date partitioning. Year-prefixed series age cleanly; one big unbounded series gets ugly fast.

Migration. When migrating from legacy systems, customers usually retain legacy numbering for migrated records and start fresh numbering for new ones — configure the series accordingly.