About ReckonDay
ReckonDay is a directory of date, time, and countdown calculators built around one idea: the easy cases of date math were never the problem. Any calculator can tell you the gap between two nearby dates. The genuinely hard part is the edge cases — a leap year landing inside a date range, a business-day count that depends on which country's weekend definition applies, a month-end date that doesn't exist in the following month, or a clock-time duration that crosses midnight.
Every calculator on this site is built on one shared, unit-tested date-math engine rather than a separate hand-rolled calculation per tool, so the same leap-year rule, the same month-end convention, and the same weekday-computation logic produce consistent answers no matter which calculator you're using. See the Methodology page for the specifics of how that engine handles the Gregorian calendar's real irregularities.
ReckonDay is built and maintained by Praveen, based in Berlin, Germany. The site doesn't require an account, doesn't store the dates you enter, and runs its calculations entirely in your browser.
The site is organized into six categories rather than one long, undifferentiated list of tools — Age & Birthday, Date Math, Time & Duration, Countdowns, Calendars, and Time Zones — because each of those domains has genuinely different edge cases worth explaining on their own terms: a birthday's leap-day convention has nothing in common with a business-day count's weekend definition, or a sleep calculator's 90-minute cycle assumption.
Beyond the calculators themselves, the site maintains a curated set of pre-built reference pages — countdowns to commonly searched dates, public holiday tables for 20 countries, a growing set of time-zone conversion pairs between commonly compared cities, a rolling "when is [holiday]" lookup covering several years ahead, printable monthly calendars, and a small blog covering the calendar-math concepts behind the tools in more depth than a single tool page allows.
The reference pages exist for the same reason the tools do: a lot of date questions have a genuinely correct, computable answer that doesn't need to be re-derived by hand every time someone asks it. "How many days until Thanksgiving," "what day of the week was the moon landing," and "what's the time difference between New York and Tokyo right now" are all questions with one correct answer at any given moment, and this site tries to answer them directly rather than making the reader do the arithmetic themselves.
What this site deliberately doesn't do: it doesn't compute movable religious or lunar holidays (Easter, Diwali, Ramadan, Lunar New Year, and similar) as if they were fixed dates, since a static table would silently go stale the following year — those are flagged clearly wherever they'd otherwise be expected rather than given a fabricated date. It also doesn't require sign-up, doesn't track individual visitors' calculation history, and doesn't sell the dates or times anyone enters into a calculator, because none of that input ever leaves the browser it was typed into.