Date Calculator (Add or Subtract Days, Weeks, Months, Years)
Accurately add or subtract calendar intervals from any starting date. Find out what day of the week a future date lands on, calculate deadlines, notice periods, and explore calendar metrics.
Interval Conversion Summary
Between start and target dateHow Date Arithmetic & Shift Calculations Work
Learn how variable month lengths, leap years, and calendar cycles are resolved in date math.
Select Starting Anchor
Pick any baseline date. You can choose today's date, an invoice issue date, a project kickoff, or an event deadline.
Choose Operation & Units
Select Add (+) or Subtract (−) and enter any combination of years, months, weeks, and days, or use quick presets (e.g. +30 days, +90 days).
Inspect Target Metrics
View the resulting date, its day of the week, weekday vs. weekend status, day number in the year, and week of the year.
How does adding a month to January 31st work?
February does not have 31 days. Our date engine automatically clamps to the last valid day of that month (February 28 in common years or February 29 in leap years).
What are common commercial uses for date calculators?
Payment term deadlines (Net 30, Net 60, Net 90), real estate escrow periods, passport expiration windows, warranty periods, and pregnancy milestone tracking.
Does this calculator count weekends or holidays?
This tool adds pure calendar days and identifies whether the result is a weekend. If you need to deduct official federal/state legal holidays and exclude all weekends, use our Business Days Calculator.
What calendar system is used?
Calculations strictly follow the International Standard Gregorian Calendar (ISO 8601), including leap year rules and standard week numbering.