Large integers are treated as milliseconds. Uses your browser timezone for local display.
The numeric field accepts a whole number. Values with absolute magnitude < 1e12 are treated as seconds since Unix epoch; larger magnitudes are treated as milliseconds. UTC ISO output uses toISOString; the local line uses your browser’s locale for display.
This calculator uses plain decimal numbers. If a result looks wrong, check whether you used a comma instead of a dot (or vice versa) where the field expects one.