Date Diff Calculator

How many days between two dates? More than a calendar glance. Fewer than it feels.

Use this free days between dates calculator to find the exact number of days from one date to another. Pick a start date and an end date and get the count — for deadlines, countdowns, age in days, contract terms, rental periods, "how long have we been doing this," and any other interval a calendar cannot answer without counting on fingers.

Date arithmetic looks trivial and is a minefield: months have 28 to 31 days, leap years exist, and February is a special case that has broken production software at every major company. We let the computer handle the calendar. That is what it is for.

What This Days Between Dates Calculator Does

Counts the days between two dates, leap years included
Works in either order — start after end still returns the positive gap
Divide by 7 for weeks, 30.44 for average months, 365.25 for years
Perfect for due dates, project timelines, vacation counts, and settling "it's been how long?" arguments

How to Use the Days Between Dates Calculator

Inputs:

Start Date — the earlier date
End Date — the later date (order does not actually matter)

Steps:

Pick the start date
Pick the end date
Click Calculate for the number of days
Need the date N days from today instead? Use the Add Days calculator

How the Calculation Works

Days = | End Date − Start Date | (in whole days) Weeks = Days ÷ 7 · Months ≈ Days ÷ 30.44 · Years ≈ Days ÷ 365.25

The count is exclusive of the start day: Jan 1 → Jan 2 = 1 day. Add 1 if you need to count both endpoints (e.g., nights vs days of a hotel stay)
Leap years (366 days) fall every 4 years, except century years not divisible by 400 — 2000 was, 2100 will not be
Business days are different: roughly Days × 5/7 minus holidays

Worked Example: March 15, 2026 → September 1, 2026

Rest of March: 16 days (16th–31st)
April 30 + May 31 + June 30 + July 31 + August 31 = 153 days
September 1: +1 → 16 + 153 + 1 = 170 days
That is 24 weeks and 2 days, or 5.6 months, or "the entire summer you said you would use productively."

Tips (From People Who Have Made These Mistakes)

For age in days, use your birth date as the start and today as the end — or the Age Calculator for the full breakdown
Contracts often specify "calendar days" vs "business days." This tool gives calendar days
Counting nights (hotels, rentals)? That is exactly the day difference. Counting days present? Add 1

Frequently Asked Questions

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

Subtract the earlier date from the later one, accounting for month lengths and leap years — or use this calculator. Example: Jan 1 to Dec 31 of the same non-leap year = 364 days.

Does the calculator include the end date?

It counts the difference, so Jan 1 → Jan 3 = 2 days. If you want inclusive counting (Jan 1, 2, and 3 = 3 days), add 1 to the result.

How many days are in a year?

365, or 366 in a leap year. On average 365.25 — which is why "days ÷ 365.25" gives a clean years figure over long spans.

How do I convert days to months?

Divide by 30.44 (the average month length) for an approximation. 170 days ≈ 5.6 months. For an exact month count, compare the actual calendar dates.

How many days until Christmas?

Depends when you ask. Put today and December 25 into the calculator — or use the Days Until calculator, which uses today automatically.

Mini Roast Disclaimer

We roast the number, not you. But if you are calculating how many days it has been since you last went to the gym, we both know the answer is "a lot."

Reality Check

The calculation uses calendar dates at midnight, so time zones and daylight saving do not affect the day count. It does not know about holidays, business days, or your specific contract's definition of "day." For legal or financial deadlines, confirm the counting convention with whoever wrote the rules.