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Home / Unix Timestamp & Epoch Tools / Timestamp Add/Subtract Calculator
Unix Timestamp & Epoch Tools

Timestamp Add/Subtract Calculator

Shift an epoch value by an integer duration locally and inspect the resulting timestamp and UTC date.

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Unix/POSIX time is based on seconds since the 1970-01-01 UTC epoch. Browser date rendering uses JavaScript Date/Intl; sub-millisecond epoch arithmetic is preserved with BigInt where the tool exposes it.

Epoch precision and display semantics stay explicit

Integer epoch arithmetic uses exact BigInt scaling where applicable. Unit choice, browser Date range and time-zone display are kept separate so a convenient output does not hide a precision or interpretation change.

Built for developer copy-and-check workflows

v264 keeps current-time shortcuts, copy actions, practical mobile controls and the governing unit/zone assumption next to the result so common log and API timestamp checks take fewer steps.

Use this result with confidence

Keep the timestamp unit explicit

Unix timestamps may be stored in seconds, milliseconds, microseconds, or nanoseconds. A value interpreted at the wrong scale can land decades away while still looking numeric. Record the unit beside the source value and confirm the displayed date before applying an offset, especially when copying data from JavaScript, databases, or telemetry systems.

Calendar arithmetic and fixed-duration arithmetic differ

Adding 24 hours is a fixed elapsed duration. Adding one local calendar day can behave differently across daylight-saving transitions. Decide whether the requirement is elapsed seconds or a wall-clock calendar change, then use the corresponding operation. For protocol timestamps, UTC duration arithmetic is usually easier to reproduce.

Watch precision when values exceed safe integer ranges

Large epoch values expressed in sub-second units can exceed the exact integer range of ordinary JavaScript numbers. If the source requires nanosecond-level identity, preserve it as an integer string or BigInt-capable value and only convert the portion needed for display. Do not infer high-resolution precision from a rounded human-readable timestamp.

Verify both directions

After adding or subtracting an offset, apply the inverse operation and confirm you return to the original timestamp under the same unit and arithmetic model. Keep the original value, offset, unit, and result together in developer handoffs so timezone display differences are not mistaken for changes to the underlying epoch value.

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