Time Since Date

Days, hours, minutes, seconds elapsed since a past date.

Inputs

Result

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General calculation reads

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Jordan Ellenberg - math thinking
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The Joy of X
Steven Strogatz - accessible math
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Scientific calculator (Casio fx-991EX)
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How to use this calculator

  • Set past date.
  • Set "as of" to today.
  • Read elapsed time.

About this calculator

Inverse of countdown-to-date. Days/hours/seconds elapsed since a past event — birthdays, anniversaries, project starts, sobriety dates, etc. Like the countdown, "as of" is an explicit input so the calculation stays pure.

Frequently asked

Same math as countdown-to-date?+
Yes — just framed differently. Countdown is "future − now"; time-since is "now − past". Both are date arithmetic.
How accurate are seconds?+
Days × 86400 — assumes every day is 86400 seconds. True except DST transitions and leap seconds (negligible).
Can I track sobriety/streaks?+
Yes — set the start date as past, "as of" as today.
How many seconds since [historical event]?+
Set both dates and read the seconds figure. Note: dates before 1970 are still valid in JavaScript.
Why average month/year?+
30.4375 days = average month (Gregorian). 365.25 = average year. For exact-month figures, use months-between-dates.

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