What format does Klaviyo require for historical event timestamps?

Klaviyo's current historical-event CSV guidance specifies a Timestamp column formatted as YYYY-MM-DD HH:mm:ss.

Why does Klaviyo report an invalid date or timestamp format?

The CSV value may not match a supported date format or the property may be mapped to an incompatible Klaviyo data type. Explicitly select the source convention and review flagged values before importing.

Private Klaviyo import preflight

Klaviyo CSV Date & Timestamp Formatter

Fix profile-property dates and historical event timestamps before importing. Check Klaviyo-specific identifiers, duplicate records, event IDs, and CSV structure without uploading customer data.

Browser-only processing No silent date guessing Klaviyo-ready CSV

Klaviyo CSV input

Drop a CSV hereor click to choose a file

or paste CSV

CSV with a header row

Every original row, empty cell, and unselected value stays in place. Output is normalized to UTF-8 comma-separated CSV.

Klaviyo import mapping

Import job The preflight applies the identifiers, column order, file limit, and duplicate rules for this job.

Load a CSV to detect likely profile date, profile timestamp, and historical event Timestamp columns.

Select date and timestamp columns

Paste or upload CSV to run the Klaviyo preflight.

Klaviyo-ready preview

Load a CSV to create a corrected preview. Your data stays on your device.

Corrected rows will appear here after you paste or upload CSV.

Klaviyo-safe output

Profile property date2026-12-31

Profile property timestamp2026-12-31 14:30:00+00:00

Historical event Timestamp2026-12-31 09:30:00

Date-only values remain calendar dates. Profile timestamps include an explicit UTC offset. Historical event timestamps use the exact second-level shape in Klaviyo's guide and are rendered in the account time zone selected above.

Fix invalid Klaviyo CSV dates and timestamps

Klaviyo recognizes specific date and timestamp representations. This tool converts the columns you select and checks the complete file for problems that can still derail profile/list and historical-event imports: missing identifiers, duplicate identifiers, event Timestamp requirements, repeated timestamps without unique event IDs, malformed CSV rows, and invalid temporal values.

Choose the Klaviyo import job

Select profile/list or historical event import so the preflight applies the correct destination rules.

Confirm date columns and time zones

Assign each column a Klaviyo destination type and choose the actual source format. Local times are never guessed through DST transitions.

Review and download

Inspect complete-job diagnostics, correct any blocked values, and download the normalized Klaviyo-ready CSV.

Klaviyo date and timestamp examples

Klaviyo destination	Example input	Output	Behavior
Profile property date	`12/31/2026`	`2026-12-31`	Calendar date preserved
Profile property timestamp	`12/31/2026 9:30 AM`	`2026-12-31 14:30:00+00:00`	America/New_York source resolved to explicit UTC
Historical event Timestamp	`2026-12-31T14:30:00Z`	`2026-12-31 09:30:00`	Rendered for an America/New_York Klaviyo account

Profile and list imports

Check the 50 MB list-import ceiling, header row, email/phone identifiers, duplicate identifiers, basic email shape, dates, and timestamps.

Historical event imports

Check the required Timestamp and customer identifier fields, email column order, and unique $event_id values when timestamps repeat.

Private customer-data cleanup

No Klaviyo login or DataZier server upload is required. Parsing, validation, transformation, preview, and CSV generation remain in browser memory.

Important Klaviyo date-only guidance

Klaviyo currently warns that a date imported without a timestamp receives midnight UTC when mapped to its Date data type, which can move date-triggered flow behavior a day earlier or later depending on timezone. For birthday-style calendar dates, Klaviyo recommends mapping date-only values to text. DataZier preserves the calendar date and leaves the final Klaviyo property mapping to you.

What this Klaviyo preflight does not check

The preflight checks CSV structure, common import identifiers, historical-event fields, and selected temporal columns. It does not inspect your Klaviyo account, consent status, property mappings, list permissions, suppression state, phone validity, ecommerce integration, custom data types, or account settings. It cannot guarantee a successful import; keep a backup and test a small batch first.

For the current source of truth, use Klaviyo’s official accepted date and timestamp formats, historical event import guide, and list import troubleshooting guide.

Klaviyo CSV date formatter FAQ

What date format should I use in a Klaviyo CSV?

Klaviyo accepts YYYY-MM-DD and MM/DD/YYYY date values. DataZier writes the unambiguous YYYY-MM-DD form.

What format should historical event Timestamp use?

Klaviyo's current historical-event CSV guide specifies YYYY-MM-DD HH:mm:ss. Select your Klaviyo account timezone so offset-bearing source values can be rendered as the correct account-local wall time.

Why are repeated historical-event timestamps flagged?

Klaviyo says rows sharing a timestamp need unique $event_id values; otherwise only one may be imported. DataZier reports missing and duplicate event IDs without inventing them.

Does DataZier upload my Klaviyo CSV?

No. CSV parsing, validation, date conversion, and download generation happen locally in your browser. Only paid-access checks use DataZier’s access endpoints.

Is the Klaviyo CSV formatter free?

Jobs with up to 50 selected non-empty date or timestamp cells can be prepared and downloaded free. Larger jobs receive a 50-change preview and require DataZier Pro for the complete CSV.

Klaviyo is a trademark of Klaviyo, Inc. DataZier is an independent tool and is not affiliated with, endorsed by, or sponsored by Klaviyo.