Date Calculator
Date Calculator
Based on your results — what to do next:
Calculate your exact age
Know the precise number of years, months, and days since your birth date — plus your next birthday countdown.
How far away is retirement?
Use these date calculations to map out exactly how many years and months until your target retirement date.
Saving toward a deadline?
Once you know how many days or months until your goal, find out exactly how much to save each month to hit it.
This date calculator has two modes: Days Between Dates finds the exact number of days, weeks, months, years, and business days between any two calendar dates; Add / Subtract Days finds what date falls a specific number of days before or after any starting date. Both modes are instant — no forms to submit. Common uses include contract deadlines, project planning, loan maturity dates, age calculations, and counting days until an event.
How Date Calculations Work
All date calculations convert dates to a Unix timestamp (milliseconds since January 1, 1970) and compute the difference. The results are then converted back into human-readable units. Business days are counted by iterating each calendar day and excluding Saturday (day 6) and Sunday (day 0).
Weeks = ⌊Total Days ÷ 7⌋
Business Days = Σ weekdays between start and end date
| Unit | Formula | Notes |
|---|---|---|
| Total Days | End − Start | Exact calendar days including both endpoints |
| Weeks | ⌊Days ÷ 7⌋ | Floor division — complete 7-day weeks |
| Years / Months / Days | Using 365.25 / 30.44 day averages | Approximation accounting for leap years |
| Business Days | Count Mon–Fri only | Does not subtract federal holidays |
Worked example: January 1, 2026 → June 28, 2026 = 178 total calendar days = 25 complete weeks + 3 days = 127 business days. If you need to add 90 days to March 15, 2026 → March 15 + 90 = June 13, 2026 (a Saturday).
💡 Pro-Tip
Legal and Financial Deadlines Are Not Optional: Many contracts, insurance policies, and tax deadlines count in business days, not calendar days. The IRS "timely mailed = timely filed" rule uses postmark date. Lease renewal windows are often 60–90 calendar days before expiration. Statute of limitations on legal claims can run to the day. Loan grace periods are calendar days. When in doubt, always use calendar days for date math — and verify with the specific agreement whether "days" means business or calendar days. Note: our business day count excludes weekends but does NOT exclude federal holidays — subtract those manually for strict business-day contracts.
Date Calculator FAQ
How many days until a specific date?
Use the "Days Between Dates" tab, set Start Date to today and End Date to your target date. The calculator shows the exact number of days, weeks, months, and business days remaining. Common uses: days until a wedding, vacation, contract expiration, tax deadline (April 15), or retirement date.
What date is 30/60/90/180 days from today?
Use the "Add / Subtract Days" tab, set today as the starting date, and enter your desired number of days. Today (June 28, 2026): +30 days = July 28, 2026; +60 days = August 27, 2026; +90 days = September 26, 2026; +180 days = December 25, 2026; +365 days = June 28, 2027.
How do I calculate someone's age in days?
Enter their birth date as the Start Date and today as the End Date in the "Days Between Dates" tab. The total days result is their age in days. For a more detailed age breakdown (exact years, months, days, plus birthday countdown), use the dedicated Age Calculator.
Why does February make date math complicated?
February has 28 days (29 in leap years), which means adding "1 month" from January 31 has no equivalent date in February. Our calculator avoids this ambiguity by working in exact days rather than calendar months for the "Add Days" function. When showing years/months/days breakdowns, we use approximate averages (30.44 days per month, 365.25 days per year) which is accurate for practical purposes.