Julian to Gregorian Converter

Applies century-dependent offsets for Old Style to New Style conversions with both directions shown. Enter 1900-01-01 Julian to get 1900-01-14 Gregorian plus reverse Gregorian 1900-01-01 to Julian 1899-12-19 with plus thirteen days noted. Bands follow Gregorian reform of October 1582 where ten days were skipped. All math runs locally with no uploads for sensitive family records.

Why offsets grow across USA colonial history: Julian calendar adds a leap every four years without exception, drifting eleven minutes yearly against the sun. Gregorian drops century leaps unless divisible by four hundred, so 1700 and 1800 and 1900 were not leap in New Style but were in Old Style. Gap was ten days 1582 to 1700, eleven to 1800, twelve to 1900, thirteen after 1900 through 2099. George Washington born February 11 1731 Old Style became February 22 1732 New Style after year-start shift.

USA adoption timeline to cite: British Empire including thirteen colonies adopted Gregorian in September 1752, skipping September 3 to 13 and moving New Year from March 25 to January 1. Russia stayed Julian until 1918, Greece until 1923, which matters for immigration manifests at Ellis Island in New York. French Louisiana used Gregorian earlier via France 1582, Spanish Florida likewise, causing dual dating in Gulf Coast parish books.

Dual dating and year-start traps: Dates January 1 to March 24 before 1752 often show 1731/32 style where first year is Old Style March-start and second is New Style January-start. This tool converts day-month offsets only and preserves entered year numbers, so adjust year manually for January through March colonial entries. Wills proved February 1731 Old Style belong to 1732 New Style in modern databases across Virginia and Massachusetts.

Privacy and accuracy for research: Year-band offsets approximate proleptic rules and work for genealogy, exhibits, and classroom timelines. For astronomical precision around 1700 leap boundaries, verify against naval observatory tables. No network means courthouse and archive use without accounts. Copy both lines into citations as Julian date arrow Gregorian date with offset noted for peer review.

Limits and pairings: Covers civil dates only without Orthodox Julian Easter tables that differ from Gregorian computus. For Easter in colonial years, run easter-date alongside after converting year context. For weekday names of converted dates, run day-of-week with the Gregorian result to confirm Sunday services and court sessions.