Year Calculator
What any year is made of — leap or common, 365 or 366 days, how it opens and closes, and how many ISO weeks and working days it holds.
Year Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Gregorian calendar only — no Julian or reform dates
- Holiday-free working-day counts
In short: 2026 is not a leap year: 365 days, February holding 28. It opens on a Thursday and closes on a Thursday — a 365-day year starts and ends on the same weekday, one weekday ahead of where a leap year would leave you. It runs 53 ISO weeks, one of the rare Thursday-opened shapes, and prices 261 working days against 104 weekend days. The century rule is why 1900 was common while 2000 was leap: divide by 100 and the leap day is withheld, unless the year also divides by 400.
Formula
leap iff y mod 4 = 0, except y mod 100 = 0, except y mod 400 = 0
The Gregorian rule keeps the calendar at 365.2425 days against the solar 365.2422. Every fourth year adds 29 February; centuries withhold it unless the year divides by 400 — 1600 and 2000 kept their leap day, 1700, 1800 and 1900 did not. A 365-day year starts and ends on the same weekday; a 366-day year closes one weekday later. Fifty-three ISO weeks arrive only when the year opens on a Thursday, or on a Wednesday in a leap year.
Worked Example
- Type a year between 1900 and 2035.
- Read the leap verdict and the day count.
- Check the opening and closing weekdays and the ISO week count.
Defaults: 2026 — not leap, 365 days, opens and closes Thursday, 53 ISO weeks, 261 working and 104 weekend days. Try 1900 for the withheld century leap day, 2000 for the kept one.
Strengths & Limits Of This Model
Where this engine is strong
- Leap verdict with the century rule explained
- ISO week count and weekday split in one read
Where it stops
- No holiday adjustments; the count is pure calendar
Practical Use Cases
Planning
how many working days a year actually holds
Curiosity
why 1900 was common but 2000 was leap
Scheduling
which weekday a year opens and closes on
Methodology & Editorial Standards
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Year Calculator — 8 Expert FAQs
8 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
Why does a 365-day year start and end on the same weekday?
Because 365 is 52 weeks plus one day. The year advances exactly one weekday from its opening; the last day lands on the same name as the first. A 366-day leap year advances two, so it closes one weekday past its opening.
When does a year run 53 ISO weeks?
Under the ISO Thursday rule: a year owns 53 weeks when it opens on a Thursday, or when it opens on a Wednesday and holds a leap day — either way December 28 ends up in the year's own 53rd week. That is about 71 years in every 400.
Can a leap year still run 52 ISO weeks?
Yes — 2024 is the standing example. It is leap, but it opens on a Monday, so the Thursday rule never trips and the year runs 52 ISO weeks. Leap status and week count are different questions.
How many working days does a year hold?
Fifty-two full weeks contribute 260 Mondays-through-Fridays; the one or two leftover days add more when they land midweek. 2026 holds 261, 2024 holds 262, 2000 held 260. Holidays are a different ledger — this is the calendar's own count.
Why the exceptions to the every-four-years rule?
The solar year runs about 365.2422 days, so adding a day every four years overcorrects by roughly three days per four centuries. Centuries withhold the leap day unless the year divides by 400, which trims the calendar back — that is the 100 and 400 in the formula.
Is 2000 a leap year?
Yes. It divides by 400, so the century withholding does not apply — 366 days, opening Saturday and closing Sunday. 1900 is the counterexample: it divides by 100 but not 400, so its leap day was withheld.
What weekday a year opens on — does it repeat?
Calendars repeat on cycles of 6, 11, 5, then 6 years across a usual 28-year stretch, broken wherever a skipped century leap day intervenes. The page computes the actual weekdays rather than leaning on the cycle.
Why does the panel stop at 1900 and 2035?
The date engine is exact across that century and a half, which covers every planning question the page is built for. The leap arithmetic itself is exact for any Gregorian year — the panel is a display boundary, not a math one.