Date Calculator.
Find days between two dates, add or subtract years, months and days from any date, and discover the day of the week for any date — past, present, or future.
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How to Use
Select a Mode
Choose Date Difference to count days between two dates, Add to Date or Subtract from Date for date arithmetic, or Day of Week to find which weekday any date falls on.
Enter Your Dates
Use the date pickers to enter your dates. Click the "Today" shortcut to instantly set today's date as a start point without typing.
View Full Results
Click Calculate for a complete result: total days, weeks, months, years, and the formatted date — all in one card.
Date Difference Formula
Core Calculation
Days = (Date₂ − Date₁) ÷ 86,400,000
(milliseconds per day)
Earlier date (as Unix timestamp in ms)
Later date (as Unix timestamp in ms)
24h × 60m × 60s × 1000ms
Worked Examples
Example 1: Days until end of year
Start: 1 April 2026 → End: 31 December 2026
- 011 April 2026 = day 91 of 2026
- 0231 December 2026 = day 365 of 2026
- 03Difference = 365 − 91 = 274 days
274 days = 39 weeks 1 day
Use this for goal setting — how many days left in the year to achieve your targets?
Example 2: Add 3 months to a date
Base date: 15 November 2025 + 3 months
- 01November + 3 months = February
- 0215 November + 3 months = 15 February 2026
- 03Day of week: Sunday
Result: 15 February 2026 (Sunday)
For quarterly deadlines, contract renewals, and subscription billing cycles.
Example 3: Age in days
Born: 10 June 1995 → Today: 29 May 2026
- 011995 to 2026 = 31 years (approx)
- 0231 × 365.25 ≈ 11,322 days (average)
- 03Exact calculation using date difference: 11,311 days
Age: 30 years 11 months 19 days = 11,311 days old
Far more precise than estimating — accounts for leap years automatically.
Complete Guide
Dates are deceptively complex. Unlike simple integers, dates must account for months of different lengths (28, 29, 30, or 31 days), leap years, and the fact that "one month" can mean different things depending on which month you start in. Adding one month to January 31st does not give you February 31st — it gives you March 2nd or 3rd (the overflow carries forward). Our date calculator handles all these edge cases correctly, using JavaScript's native Date object which fully accounts for the Gregorian calendar including leap year rules.
Pro Tip: For legal contracts and financial agreements, always use "calendar days" explicitly. Whether a 30-day notice period includes the start date varies by jurisdiction — when in doubt, use the exact end date from this calculator and specify it in your agreement.
The Four Modes and When to Use Each
Date Difference answers "how far apart are these two dates?" It returns the total number of calendar days, the same span expressed in weeks (with remainder days), and a natural breakdown in years, months, and days. This is the mode for calculating age, time until a deadline, days elapsed since an event, or duration between two calendar milestones.
Add to Date answers "what date is X days/months/years in the future from a given starting point?" It is essential for calculating contract end dates, subscription renewal dates, legal notice periods, project milestones, and any future event calculation. You can add a combination of years, months, and days simultaneously.
Subtract from Date is the reverse — "what date was X days/months/years before a given date?" Useful for determining when a process should have started to meet a deadline today, calculating backdated dates, or finding historical reference points.
Day of Week answers the frequently-asked question "what day of the week does a specific date fall on?" This is useful for scheduling (ensuring an event doesn't fall on a weekend), historical curiosity (what day of the week were you born?), and planning recurring events.
Date Arithmetic: Common Pitfalls
The most common error in manual date calculations is month-end overflow. Adding one month to January 31 manually, people often write "February 31" — which doesn't exist. The correct result depends on convention: some systems round down to the last day of February (28th or 29th), while others carry over to March 2nd/3rd. Our calculator uses JavaScript's built-in Date arithmetic, which carries the overflow forward to the next month.
Leap years are another source of errors. 2024 was a leap year with 366 days. 2026 is not — it has 365. If you are calculating days over a period that spans February 29th, you must account for whether the specific year in question is a leap year. Our calculator handles this automatically.
Practical Use Cases in India
Income tax deadlines: India's assessment year runs from 1 April to 31 March. Use Date Difference to count days remaining until ITR filing deadlines. GST return due dates: GSTR-3B is due by the 20th of each month. Use Add to Date to calculate the next N due dates. Fixed deposits: Calculate the exact maturity date by adding the tenor (e.g. 1 year 3 months) to the FD start date. Leave encashment and notice periods: HR teams use date calculators to calculate exact notice period end dates for resignations, calculate leave balances, and determine probation completion dates.
EMI schedules: Add 1 month to the disbursement date to find the first EMI due date. Add the loan tenure in months to find the last payment date. SIP investment tracking: Track exactly how many months you have been investing in a SIP and when your targeted period ends. Property registration and possession: Real estate agreements specify possession timelines in months — use our calculator for exact dates.
Calendar Days vs. Business Days
Our calculator counts calendar days — all 365 (or 366) days in a year, including weekends and public holidays. For banking, legal, and HR contexts in India, you may need business days specifically. Business days typically exclude Saturdays, Sundays, and gazetted public holidays. For precise business-day calculations in regulated industries, consult the relevant regulatory calendar (RBI, SEBI, etc.) or your legal advisor.
For general scheduling — "is this deadline a weekend?" — the Day of Week mode is invaluable. If a deadline falls on a Sunday, you typically want to move to the prior Friday or the following Monday depending on the context.
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Date Calculator FAQ Hub
Everything you need to know about date calculations.
1. How do I calculate days between two dates?
Use Date Difference mode. Enter start and end dates, click Calculate. Get total days, weeks, and Y/M/D breakdown instantly.
2. How do I add days to a date?
Use Add to Date mode. Enter base date + years/months/days to add. Result shows the exact future date and day of week.
3. What day of the week is a specific date?
Day of Week mode. Enter any date, click Calculate. The result highlights the day on a visual week display.
4. How do I calculate a deadline date?
Add to Date mode. Enter today (use the Today shortcut) + deadline duration (e.g. 30 days or 3 months).
5. How many days are in a year?
365 in a common year, 366 in a leap year. Leap years are divisible by 4 (except century years not divisible by 400).
6. How do I calculate age in days?
Date Difference mode. Start = birth date, End = today. The total days is their exact age in days.
7. What is the difference between calendar and business days?
Calendar days count every day. Business days exclude weekends and holidays. Clarify which applies for contracts or deadlines.
8. How many days until an event?
Date Difference mode. Start = today (use Today shortcut), End = event date. Result = days remaining.
9. How do I subtract months from a date?
Subtract from Date mode. Enter base date and set Months to subtract. E.g. 6 months before 1 July 2026 = 1 January 2026.
10. What date is 100 days from today?
Add to Date mode. Click Today → enter 100 in Days → Calculate. Instantly shows the date 100 days ahead.
11. How many weeks between two dates?
Date Difference result includes total weeks and remaining days. 365 days = 52 weeks 1 day.
12. What is India's fiscal year range?
India FY runs 1 April to 31 March. FY 2025-26 = 1 April 2025 to 31 March 2026 = 365 days.
13. How do I calculate a pregnancy due date?
Add to Date mode. Enter LMP (first day of last period) + 280 days. Consult your doctor for medical guidance.
14. 30 days vs 1 month — are they the same?
No. 1 month from 31 January = 28/29 February. 30 days from 31 January = 2 March. Use Days for exact counting.
15. What is the difference between date and age calculator?
Date calculator is general-purpose for any two dates. Age calculator specialises in calculating exact current age from a birthdate.
16. Can I calculate past dates?
Yes. Use Subtract from Date mode or enter historical dates in Date Difference mode. Supports dates going back centuries.
17. What day of the week was I born?
Day of Week mode. Enter your birth date, click Calculate to see exactly which weekday it was.
18. How accurate is the date calculator?
Uses JavaScript's built-in Date object, correctly handling leap years and all month lengths. Accurate to the day for any date.
19. How do I calculate contract expiry?
Add to Date mode. Enter contract start date + duration (e.g. 1 year or 6 months). Result is the exact expiry date.
20. What is the maximum/minimum date supported?
Our calculator supports any date JavaScript's Date object handles — roughly from year 100 AD to year 275,760 AD, more than enough for any practical use.