Bank dates without a year: handle December–January boundaries

Do not add the current year automatically to a bank date printed as 31/12. Use the document’s stated period and the original row sequence. A statement crossing New Year needs at least two possible years; a file name alone is weak evidence.

Establish the period before completing years

1. Record the complete period heading and raw dates before conversion. Check whether the document covers one account and one continuous period.

2. Assign a year only when the period and row give a single supported interpretation. Store the derivation separately from the original date.

3. Flag rows outside the period or with conflicting evidence. Do not repair them simply by moving them to the nearest year.

Fictional example

A fictional statement covers 20 December 2025–19 January 2026. Rows 31/12 and 02/01 become 2025-12-31 and 2026-01-02 after source confirmation. Adding 2026 to both would move the December payment exactly one year forward (365 days here). A cropped page without its period heading stays unresolved.

Decide from candidates, then convert

A useful review table keeps the raw date, date-column heading, possible complete dates and the source of the period. For the fictional period above, 31/12 has only 2025-12-31 inside the interval; 02/01 has only 2026-01-02. By contrast, 19/12 has no candidate inside that interval. Mark it for review rather than silently changing the day or extending the period.

Use this as a proposed decision rule: one supported candidate can be accepted; none requires checking the source; two remain ambiguous. A hypothetical combined statement from 1 December 2025 to 31 January 2027 contains both 2025-12-31 and 2026-12-31. The period alone cannot choose between them. Recover a dated page heading or a bank export with complete dates. If neither is available, retain 31/12 as raw text and leave the complete date empty with an explicit unresolved status.

Apply the interval to the column it actually describes. Do not force a value date into a booking-date period merely to make it fit. Preserve the original order as supporting evidence, but first check whether it is ascending or descending; sorting incomplete dates first destroys that clue.

Only after deciding the year should you parse the complete value. Choose the date pattern and locale from the confirmed source convention; automatic parsing cannot supply evidence for an absent year.

Record the decision for every incomplete date

For the fictional 20 December 2025–19 January 2026 booking period, use a sheet like this before formatting cells as dates. The interval is inclusive in this example; confirm the document’s own boundaries first.

Printed booking date	Candidate within the period	Decision	Evidence still needed
31/12	2025-12-31	Accept after checking the heading	Page and period heading
02/01	2026-01-02	Accept after checking the heading	Same account and period
19/12	None	Hold the row for review	Complete page or corrected source reading
29/02	None	Hold the row for review	Confirm day, month and document period

Keep the decision attached to the source row, not its current spreadsheet position. A later sort must carry the raw date, complete date, column type and review status together. For a missing cover page, ask for the complete statement or use an authorised bank export covering the same account and period; the download date is not a substitute for the transaction year.

Do not infer a new year at every decrease in month number. A descending statement naturally goes from January back to December, and a summary section can restart its own sequence. First separate transaction sections from summaries. If one row contradicts its neighbours, hold that row and inspect the page instead of shifting all subsequent dates. Accept the delivery only when every completed year has evidence and every unresolved date remains identifiable.

Checks and limits

Test the first and last dates and the actual year transition. Validate leap days against the confirmed year. Keep a missing year distinct from a date-parsing failure. A spreadsheet may accept a guessed date without warning; successful conversion does not supply evidence.

Keep the original file unchanged and record any unresolved item before using the table.

Related checks

Derive a missing year from the documented period and date column. Is 03/04 March or April? Resolve ambiguous bank CSV dates · Booking date and value date: keep both in a bank statement export · Check a bank statement balance without hiding extraction errors.

BankStatementScan is in preparation. The site offers an access request and a fictional example; it does not currently convert your bank files. See the planned service.

Sources consulted on 16 October 2026

• RFC 3339 — Dates and timestamps.
• W3C — Metadata Vocabulary for Tabular Data.