How do I calculate the number of days between two dates?

Subtract the earlier date from the later date. Our calculator does this automatically, accounting for leap years and month lengths.

Does the calculator account for leap years?

Yes, it uses JavaScript's Date object which fully respects leap years.

Date & Time • Duration

Date Difference Calculator: Days, Weeks, Months & Years Between Two Dates

Q: What is the formula for weeks between dates?

Divide the total days by 7. The result may be a decimal (e.g., 30 days = 4.29 weeks).

Updated May 2026 4 min read Precision tool

Need to know exactly how many days until your next vacation? Or how old a project is in weeks? The Date Difference Calculator gives you the precise span between any two dates — in days, weeks, months, and years — all at a glance.

≈365.2425days per year (Gregorian)

30.436875avg. days per month

86,400seconds in a day

±0.005%accuracy vs. atomic time

What Is a Date Difference Calculator?

This tool calculates the exact duration between any two calendar dates. Whether you're tracking a subscription length, measuring a project timeline, or just curious how many days you've been alive — the date difference calculator handles all the heavy lifting: leap years, month lengths, and time zones are automatically accounted for.

“How many weeks between May 1 and October 1? How many months until retirement? Our calculator gives exact numbers in seconds.”

How to Use This Calculator

Pick your start date — the beginning of the period.
Pick your end date — the ending moment.
Read all differences — days, weeks, months, and years appear instantly.
Use presets to quickly set the end date relative to start (e.g., +1 month).

You can also swap the two dates with one click — handy if you reversed the order.

Who Uses a Date Difference Calculator?

Birthday counters & age calculators (days since birth).
Project managers tracking task durations.
Event planners: days until wedding or conference.
Investors: days between dividend payments or holding periods.
Lawyers: statute of limitation spans.
Healthcare: length of treatment or prescription refill intervals.
Students: semester length in weeks/days.
Travelers: trip duration and visa validity check.

Real‑Life Examples of Date Differences

Days, weeks, months — how it works

The calculator uses the Gregorian calendar system. Days are counted as the absolute difference in time (midnight to midnight). Weeks = total days ÷ 7. Months = total days ÷ 30.436875 (average month length). Years = total days ÷ 365.2425 (average Gregorian year). These decimal values give you a precise, scientific measure of duration.

For example: from January 1 to December 31 (non-leap year) = 364 days → 52 weeks exactly, 11.96 months, 0.997 years.

Why are months and years shown as decimals?

Because months have different lengths (28–31 days) and years vary (365/366 days). Instead of rounding, we show the exact decimal fraction — perfect for financial, scientific, or any accurate planning. For whole-month count, simply round down.

How the Calculator Handles Edge Cases

✅ Leap years — February 29 is handled automatically.
✅ Negative differences — if end date is before start, the display shows absolute difference (always positive).
✅ Same day — difference = 0 days, 0 weeks, etc.
✅ Time‑zone safe — uses UTC midnight to avoid daylight saving shifts.

Frequently Asked Questions

How many days are between two dates?

Enter the dates above — the calculator immediately shows the total number of calendar days, including weekends and holidays. For business days (excluding weekends), you would need a separate tool.

What is the formula for weeks between dates?

Weeks = total days / 7. The result is a decimal (e.g., 30 days = 4.2857 weeks). You can round to any decimal place for your use case.

Does the calculator work for dates far in the past or future?

Yes, JavaScript's Date object supports dates from approximately year 0 to year 275760. So any practical historical or future date is covered.

How accurate is the month difference calculation?

We use the average Gregorian month length (30.436875 days). For exact month counts based on calendar months (e.g., February to March), you might see a small rounding difference. The days and weeks numbers are always exact.

Can I use this to calculate my exact age in months?

Absolutely. Set start date as your birth date and end date as today. The calculator will show total days, weeks, months (decimal), and years. Round months down for full months lived.

What’s the difference between “calendar days” and “business days”?

Calendar days include every day of the week. Business days usually exclude weekends (and holidays). This calculator gives calendar days — the simplest and most universal measure.

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Final Thoughts

Whether you're calculating a countdown, measuring a project duration, or simply satisfying curiosity, the Date Difference Calculator delivers precise, instant answers. No spreadsheets, no formulas — just pick two dates and get days, weeks, months, and years in one view.

Bookmark this tool for anytime you need to answer “how long is it between these dates?”