Date Difference Calculator
Calculate exactly how many days, weeks, months, and years are between any two dates. Perfect for deadlines, anniversaries, age calculations, and project planning.
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Date Calculation Guide
What's the difference between Days and Working Days?
Calendar days count every day including weekends and bank holidays. Working days (also called business days) count only Monday to Friday. A 30-day period typically contains 22 working days. For contract deadlines, payment terms, and regulatory timeframes, check whether 'days' means calendar or working days — in law and finance, it often means calendar days unless otherwise specified, but employment-related deadlines (P45, notice periods) typically use calendar days.
What should I know about Counting Months and Years?
Month-based calculation is more complex than day-based because months have different lengths. Going from January 31 to February 28 is one month, but 28 days. Going from January 1 to February 1 is also one month but 31 days. The ISO 8601 standard defines date arithmetic: months are counted by calendar position, not day count. For financial calculations (compound interest, loan amortisation), use exact day counts rather than month approximations.
What should I know about Common Date Calculations?
Notice periods (employment): typically 1 week per year of service (minimum), up to the contractual notice period. Start counting from the day after the notice is given. Project deadlines: if a project is '90 days', check whether this means calendar or working days — 90 working days is approximately 18 weeks vs 90 calendar days = ~13 weeks. Visa and passport validity: many countries require 6 months' validity beyond your travel dates — count carefully.
What do I need to know about Age and Anniversary Calculations?
Age calculations count complete years from birthday to the current date (or any target date). The leap year effect: someone born on February 29 officially celebrates their birthday on March 1 in non-leap years in most jurisdictions. Calculating a 25th anniversary from a given date involves adding exactly 25 years — if the original date was a leap day, the anniversary falls on March 1 or February 28 depending on jurisdiction and preference.