Find days between dates, add or subtract days, calculate business days
| Month | Days |
|---|---|
| January | 31 |
| February | 28 (29 in leap years) |
| March | 31 |
| April | 30 |
| May | 31 |
| June | 30 |
| July | 31 |
| August | 31 |
| September | 30 |
| October | 31 |
| November | 30 |
| December | 31 |
Days Between: Enter a start and end date to find the exact number of calendar days, business days (weekdays), weeks, and months between them. Works for past and future dates.
Add / Subtract: Start from any date and add or subtract a number of days, weeks, months, or years. The calculator handles month boundaries, leap years, and varying month lengths automatically.
Weekday Finder: Enter any date to find what day of the week it falls on (or fell on, or will fall on).
| Duration | Days | Weeks |
|---|---|---|
| 1 month (average) | 30.44 | ~4.35 |
| 1 quarter | ~91 | 13 |
| 6 months | ~182 | 26 |
| 1 year | 365 (366 leap) | 52.14 |
| 90 days | 90 | 12.86 |
| 180 days | 180 | 25.71 |
| 1000 days | 1000 | 142.86 |
How many days between two dates?
Use the "Days Between" tab above. Enter your start and end dates and click Calculate. The result shows calendar days, business days, weeks, and months between the two dates.
How do I add days to a date?
Use the "Add / Subtract" tab. Enter a start date, select "Add", enter the number of days (or weeks/months/years), and click Calculate. The calculator handles month lengths and leap years automatically.
How do I calculate business days?
Business days exclude weekends (Saturday and Sunday). Use the "Days Between" tab — it automatically calculates both calendar days and business days for you.
How many days are in each month?
Most months have 30 or 31 days. February has 28 (29 in leap years). See the reference table above for all months.
What is a leap year?
A leap year occurs every 4 years (366 days, with Feb 29). Exception: years divisible by 100 are not leap years unless also divisible by 400. So 2028 is a leap year, 2100 is not, and 2400 is.
How many weeks are in a year?
A regular year has 52 weeks and 1 day. A leap year has 52 weeks and 2 days.
How do I find what day of the week a date is?
Use the "Weekday Finder" tab. Enter any date and click Find Weekday to see what day it falls on.
How many days until a specific date?
Use the "Days Between" tab. The start date defaults to today — just enter your target date to see the countdown.
Calculating the number of days between two dates is a common task for project planning, billing cycles, contract deadlines, and personal milestones. Here is a step-by-step guide to doing it manually — or instantly with the calculator above.
Step 1 — Write both dates in the same format. Use a consistent format such as YYYY-MM-DD (e.g., 2026-01-15 and 2026-04-19) to avoid confusion between month and day order.
Step 2 — Convert to a day count. Count the total days from a fixed reference point (like January 1 of the year) for each date. Most programming languages and spreadsheet apps have built-in functions for this.
Step 3 — Subtract the earlier date from the later date. The result is the number of calendar days between them. For example, from January 15 to April 19 = 94 days.
Step 4 — Adjust for business days if needed. Remove weekends by dividing the span into full weeks (each contributing 5 business days) and counting remaining weekdays individually.
Step 5 — Account for holidays. If your use case requires excluding public holidays (e.g., payroll or legal deadlines), subtract them from the business day count manually.
The date calculator above handles all of this automatically. It also shows weeks, months, and years alongside the raw day count — useful for expressing long time spans clearly. For time-based calculations, see the Time Calculator.
Calendar days count every day of the week including weekends and holidays. If a contract says "deliver in 30 calendar days from April 1," the deadline is May 1 regardless of how many weekends fall in between.
Business days (also called working days) count only Monday through Friday, skipping Saturdays and Sundays. Some definitions also exclude public holidays, though this varies by country and industry. If the same contract used "30 business days," the deadline would shift to approximately May 13 — nearly two weeks later.
Why it matters for contracts: Legal and commercial agreements frequently specify business days for notice periods, payment terms, and response deadlines. Misreading "business days" as "calendar days" is a common and costly mistake.
Why it matters for shipping: Courier services quote transit times in business days. A "5-business-day" shipment dispatched on Thursday will typically arrive the following Thursday or Friday — not the following Tuesday.
Why it matters for payroll: Payroll teams calculate pay periods and payment processing lead times in business days to ensure funds settle before weekends. Use the calculator above to count business days precisely between any two dates.
Calculating age from a birthday
To find someone's exact age, calculate the days between their birth date and today, then divide by 365.25 (accounting for leap years). For a cleaner result, count the number of complete years, then add remaining months and days. Our Age Calculator does this in one click.
Finding due dates
Pregnancy due dates are typically calculated by adding 280 days (40 weeks) to the first day of the last menstrual period. For project deadlines, add the agreed number of working days to the contract start date using the Add/Subtract tab above. Knowing the exact due date helps teams plan milestones, deliverables, and buffer time effectively.
Counting working days for payroll
Payroll periods are almost always defined in business days. To calculate how many working days fall in a given month or pay period, use the Days Between tab: enter the first and last day of the period and read the Business Days figure from the result. A standard month contains roughly 20–23 business days depending on weekends and holidays.
Countdown to events
Set today as the start date and your target event date as the end date to get an instant countdown in days, weeks, and months. Useful for travel planning, exam prep, subscription renewals, and contract expiry notices.
Epoch and Unix timestamps
Developers often need to convert between human-readable dates and Unix timestamps (seconds since January 1, 1970). For that, use the Epoch Converter alongside this date calculator.
How do I calculate how many days old I am?
Enter your birth date as the start date and today as the end date in the Days Between tab. The result shows your exact age in days, weeks, months, and years. Alternatively, use the dedicated Age Calculator for a more detailed breakdown.
How do I calculate a project deadline 90 business days from today?
Use the Add / Subtract tab. Enter today as the start date, select "Add", enter 90, and choose "Days". That gives you the calendar date. Note that the result will be calendar days — if you specifically need 90 business days, count forward excluding weekends using the Days Between tab iteratively, or plan for approximately 90 ÷ 5 × 7 = 126 calendar days as a rough guide.
What is the difference between date duration and date difference?
They mean the same thing in most contexts: the number of days (or other units) between two dates. "Duration" is more common in project management and scheduling, while "difference" is used in mathematics and programming. Both are calculated by subtracting the earlier date from the later date.
How do I calculate the number of months between two dates?
Divide the total days between the two dates by 30.44 (the average number of days per month). For example, 365 days ÷ 30.44 ≈ 12 months. Our calculator shows this automatically in the Days Between result grid. For precise month counts (e.g., from March 1 to June 1 = exactly 3 months), count full calendar months instead.