Date Calculator Add / subtract / convert
What date is 1000 days from today? How many years and months is 500 days? How far apart are two dates? All three scenarios in one tool — leap years and 30/31-day months handled automatically.
Common scenarios
- 1000 days from today? — Mode 1 (Date ± N days) → "+ N days" → enter 1000. Result date + weekday + approximate years/months auto-shown.
- 100 days ago? — Mode 1 → "− N days" → enter 100. For relationship anniversary recall, school countdown.
- How long is 500 days? — Mode 2 (Days → Y/M/D) → enter 500. "About 1 year 4 months 15 days" + weeks/hours/minutes.
- Days between two events? — Mode 3 (Between two dates) → both dates. For more advanced countdown features, see the Korean Holidays calendar.
📌 Official Sources · References
- Korea National Law Information Center — Civil Code Articles 155-161 (Calculation of Periods) · Korean legal standard for calculating contract deadlines, statutes of limitations, and statutory expiration (day/week/month/year units, exclusion of the first day)
- ISO 8601 — Date and Time Format International Standard · The YYYY-MM-DD input/display format used by this tool
- timeanddate.com — Time Zone & Calendar Reference · Cross-reference for time zones, business days, and public holidays not handled by this calculator
This tool performs simple calendar arithmetic. Time zones, business days, Korean public holidays, and tax-filing deadlines are separate variables. For legal contract deadlines and statutes of limitations, the Korean Civil Code §155-161 calculation principles apply (first-day exclusion, etc.). Verify with a lawyer or the Ministry of Government Legislation (Korea Legal Information) for precise statutory periods.
Frequently asked questions
What date is 1000 days from today?
Use mode 1 (Date ± N days) with today as the start date and 1000 as the day count, "+ N days" selected. The exact date depends on which day you check, but 1000 days is roughly 2 years and 8.9 months. Same logic works for 100-day, 200-day, or any anniversary count.
How many years and months is 500 days?
Use mode 2 (Days → Y/M/D) and enter 500. The result is "about 1 year 4 months 15 days". If you specify a start date, the conversion uses calendar arithmetic with leap-year correction; without a start date it uses average values (1 year = 365.25 days, 1 month = 30.44 days). Weeks, hours, and minutes are also shown.
How is this different from a D-day calculator?
D-day calculators focus on countdown ("days remaining until target date" with D-100, D+200 format) plus saved events for tracking multiple anniversaries. This date calculator focuses on date arithmetic (add, subtract, convert). They complement each other — use the date calculator for one-off math, use a D-day-style tool when you need persistent countdown.
Are leap years and 30/31-day months handled?
Yes. The tool uses the JavaScript Date object, so leap years (4-year, 100-year, 400-year rules) and the actual length of each month (28-31 days) are automatically respected. In Mode 2 without a start date, the result uses average values (1 year = 365.25 days); with a start date the result is exact (e.g., "2026-01-01 + 500 days = 2027-05-16").
Are my inputs stored?
No. Inputs are not sent to any server and are not saved in localStorage. The Share button puts the mode/start date/day count in the URL only when you explicitly click it. 100% client-side processing.
What date range is supported?
1900-01-01 through 2100-12-31. Out-of-range inputs are blocked at the input level. Very large day counts (100,000+) may exceed practical accuracy — verify against a calendar app for critical dates.