Why this site treats a month as 30 days
The conversion factors used by the unit converter and difference calculator, why a month is 30 days and a year is 365, and when that estimate is the wrong tool.
Units
The factors on the converter
Seconds, minutes, hours, days, and weeks are exact in ordinary civil time: 60, 60, 24, 7. Months and years are not exact. This site uses 1 month = 30 days and 1 year = 365 days so that typing “2” and “months” always produces the same millisecond value.
That is a convenience for “about two months ago”, not a calendar. February has 28 or 29 days. March has 31. “1 month ago” from 31 January is not 31 December on a civil calendar; on this site it is 30 × 24 hours earlier, which lands on a different date than “last calendar month, same day number”.
What /1-month-ago actually subtracts
2,592,000 seconds (30 × 86,400). From 2 September 2026 12:00 it lands on 3 August 2026 12:00, not 2 August. If you needed “the 2nd of last month”, that is a calendar operation. Use the difference calculator with 2026-08-02 and 2026-09-02, or use a real calendar.
Years
1 year ago is 365 days. Leap days are ignored. From 1 March 2025, 365 days back is 1 March 2024 in a non-leap span; across 29 February the civil anniversary and the 365-day mark can disagree by one day. Do not use this site to compute age in law.
What to use instead
Need elapsed time between two named datetimes → time difference calculator, trust the days/hours/seconds rows, treat months/years as estimates.
Need “same date last month” → a calendar, not an offset.
Need a rough lookback for a log → /1-month-ago is acceptable if you say it is 30 days.
Conversion factors this site uses
Exact until month and year, which are labeled estimates.
- 1 minute
- 60 seconds
- 1 hour
- 3,600 seconds
- 1 day
- 86,400 seconds
- 1 week
- 7 days
- 1 month
- 30 days (estimate)
- 1 year
- 365 days (estimate)
Questions
Will you add real calendar months?
Not on the simple offset pages. Those pages are elapsed-time tools. Calendar months need a start date, which is a different product: the difference calculator with two datetimes.