Enter a start and end date to find the number of days between them.
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Add or subtract years, months, weeks, and days from a starting date.
A date calculator is an online tool that performs arithmetic on calendar dates — something that turns out to be far more complex than ordinary arithmetic because months have different lengths, leap years shift February by a day, and the Gregorian calendar's irregular structure makes it impossible to simply add or subtract numbers the way you would with ordinary quantities. Our date calculator offers two core functions: finding the difference between two dates (expressed in days, weeks, months, and years), and adding or subtracting a duration from a starting date to find a resulting date.
These tools are used daily by professionals and individuals alike: project managers calculating sprint lengths and delivery timelines, legal professionals counting days for filing deadlines, HR departments calculating employee tenure and benefit eligibility dates, teachers planning academic schedules, and expectant parents tracking pregnancy milestones. Wherever precise date arithmetic is needed, a reliable date calculator removes the risk of mental arithmetic errors.
The simplest way to count the days between two dates is to subtract one from the other in terms of elapsed calendar days. This gives a raw count of days, which our calculator then expresses in multiple units so you can choose the most meaningful representation for your purpose.
The base result — the total number of calendar days between the start and end dates — is calculated by finding the difference in milliseconds between midnight on the start date and midnight on the end date, then dividing by 86,400,000 (the number of milliseconds in one day). By default, the end date itself is not counted; only the days that have fully elapsed between the two dates are included. If you want to count both the start and end dates as full days, check the "Include end day" option to add one day to the total.
Beyond the total day count, the calculator also expresses the difference as a combination of years, months, and remaining days. This breakdown uses calendar arithmetic rather than fixed-length approximations: one calendar year is 365 or 366 days (depending on whether it includes a leap year), and one calendar month is 28, 29, 30, or 31 days depending on which month it is. The result is an exact breakdown — for example, "2 years, 3 months, 14 days" — that accounts precisely for the calendar structure of the dates involved.
The calculator also expresses the total in weeks plus remaining days. This is useful for planning recurring weekly events, payroll cycles, or any other weekly cadence. The total days are simply divided by 7 (integer division), with the remainder expressed as additional days.
The "include end day" checkbox adds one day to the total count. This matters in contexts where you want to count both the first and last day as full days. For example, a training program running from Monday to Friday inclusive is five days — but without including the end date, the calculation would return four (Friday minus Monday = 4 elapsed days). Contract periods, subscription durations, and event planning commonly require the inclusive count.
Calendar days count every day of the week, including weekends. Business days (also called working days) count only Monday through Friday. The difference can be significant over longer periods: a stretch of 30 calendar days contains only about 21–22 business days, depending on where weekends fall.
The date difference calculator automatically shows the business day count in its results whenever you select the holiday settings option. You can also exclude specific public holidays from the count, so the result reflects the actual number of working days within a period — a critical distinction for payroll, contract compliance, and project scheduling.
The calculator includes 14 commonly observed holidays that can be individually selected or deselected:
You can also add your own custom holidays by entering a name, month, and day in the custom holiday rows. This is useful for regional holidays, company-specific closures, or any recurring annual date you want to exclude from a working-day count.
The second calculator solves a different problem: given a starting date and a duration, what is the resulting date? This sounds simple but requires care because month arithmetic doesn't behave like regular number addition.
Adding months to a date follows calendar logic rather than fixed-day logic. Adding one month to January 31 does not yield "31 days later" — it yields February 28 (or February 29 in a leap year), because February does not have a 31st day. This "end-of-month clamping" behavior matches the convention used in contract law, financial instruments, and most date-handling software.
When the "Calculate in business days" option is checked, the days field is counted in business days rather than calendar days. You can choose to exclude weekends only, or weekends plus selected holidays. Years, months, and weeks remain in calendar units, but the day count skips non-working days.
The Gregorian calendar, introduced by Pope Gregory XIII in 1582 and now used as the international standard, is a solar calendar designed to keep the average calendar year aligned with the astronomical year of approximately 365.2425 days. It achieves this through a system of leap years: every year divisible by 4 is a leap year with 366 days, except for years divisible by 100 — unless also divisible by 400. This means 1900 was not a leap year but 2000 was.
The irregular month lengths — 28, 29, 30, or 31 days — mean that date arithmetic can never be reduced to simple number addition. A month is not 30 days; a year is not 365 days. Every date calculation must account for the specific months and years involved, which is why a dedicated date calculator is far more reliable than estimating manually.
Project managers use date calculators constantly: when does a 90-day sprint end? How many business days remain before a regulatory filing deadline? If a project must ship in 18 weeks, what calendar date does that correspond to? The Add/Subtract calculator answers all of these questions in seconds.
Legal deadlines are often expressed in calendar days from a trigger event: "the respondent has 30 days to reply," "the option must be exercised within 60 days of notice." Counting these manually is error-prone, especially across month boundaries. A date calculator gives precise, defensible results.
How old is someone exactly? How long has an employee been with the company? The date difference calculator gives exact breakdowns in years, months, and days — which is important for benefit eligibility, pension vesting schedules, and legal age requirements.
Many financial instruments use day counts in their interest calculations. Bond interest, loan interest, and late payment penalties are often calculated on an "actual/365" or "actual/360" basis, both of which require knowing the exact number of calendar days between two dates.
How many days until an event? How many weeks remain before a holiday? These are everyday questions that a date calculator can answer instantly, whether you're planning a wedding, tracking a year-long goal, or counting down to a vacation.
Enter your start and end dates in the Days Between Two Dates calculator above and click Calculate. The result shows the total calendar days plus the breakdown in years/months/days, months/days, and weeks/days. Check "Include end day" if you want to count both the first and last day.
Calendar days count every day of the week including weekends. Business days count only Monday through Friday. Over a 30-day period there are typically 21–22 business days. Enable "Count holidays" in the Holiday Settings to also exclude specific holidays from the working-day count.
Because February does not have a 31st day. The standard convention is to clamp the result to the last valid day of the target month. So January 31 + 1 month = February 28 (or 29 in a leap year), not March 2.
When a fixed-date holiday falls on a Saturday, it is observed on the preceding Friday. When it falls on a Sunday, it is observed on the following Monday. Floating holidays like Thanksgiving always fall on weekdays by definition. The calculator applies these rules automatically for any year.
Use the Add/Subtract calculator. Enter today's date, select Add, enter 30 in the Days field, and check "Calculate in business days." Then choose "Exclude weekend and holidays" if needed. The result is the exact date 30 business days from today.
Yes. Both the holiday settings panels include custom holiday rows where you can enter a holiday name, select a month, and select a day. Click "+ Add more inputs" to add additional rows. Custom holidays are excluded alongside the predefined ones when calculating business days.