liminfoDate Calculator
Free web tool: Date Calculator
Day Difference
0 days
Absolute
0 days
Weeks
0w 0d
Months (approx)
0 months
About Date Calculator
The Date Calculator provides two core functions: calculating the difference between two dates, and adding or subtracting a number of days from a base date. In "Date Difference" mode, select a start date and an end date to instantly see the gap expressed as number of days (signed), absolute days, weeks and remaining days, and approximate months and years. In "Add/Subtract Days" mode, choose a base date and a number of days to add or subtract, and the tool shows the resulting date along with its day of the week.
This tool is practical for anyone who needs to count days between events — project deadlines, contract periods, anniversaries, age calculations, or planning travel. Professionals in legal, financial, and project management fields regularly need exact day counts between dates, such as the number of days remaining in a lease or the exact duration of a billing period. The result also shows weeks, which is useful for scheduling recurring events.
All calculations are performed entirely in your browser using JavaScript Date objects. Date differences are computed as the number of milliseconds between two dates divided by 86,400,000 (ms per day), then rounded. Day addition/subtraction works by adding or subtracting the appropriate number of milliseconds to the base date timestamp. The tool is bilingual (Korean/English), supports dark mode, and requires no server interaction.
Key Features
- Two calculation modes: Date Difference and Add/Subtract Days
- Date Difference mode shows signed days, absolute days, weeks + remaining days, and months
- Add/Subtract mode computes the result date with day of the week displayed
- Supports both adding (+) and subtracting (-) any number of days from a chosen base date
- Uses JavaScript Date millisecond arithmetic for precision across month and year boundaries
- Today's date pre-filled as the default in all date inputs for quick use
- Bilingual Korean/English interface with Korean weekday names (일·월·화·수·목·금·토)
- 100% client-side — no data sent to any server, works offline, completely free
Frequently Asked Questions
How do I calculate the number of days between two dates?
Select "Date Difference" mode, then pick your start date and end date using the date inputs. The calculator instantly shows the difference in days (positive if the end is after the start, negative if before), the absolute number of days, the equivalent in weeks and remaining days, and the approximate number of months.
How do I find what date is 100 days from today?
Select "Add/Subtract Days" mode, set the base date to today (which is pre-filled by default), enter 100 in the days field, choose "Add (+)", and the result date will appear immediately along with the day of the week. You can also subtract days by selecting "Subtract (-)".
Does the calculator account for leap years?
Yes. All calculations use JavaScript Date objects which fully account for leap years, different month lengths, and daylight saving time transitions. The millisecond-based arithmetic means that every day addition or subtraction is accurate regardless of the months or years spanned.
What does "weeks and remaining days" mean?
The date difference result includes a weeks format: for example, 45 days is shown as "6 weeks 3 days". This is calculated by dividing the absolute number of days by 7 (integer division for weeks, and the remainder for remaining days). It is useful for planning on a weekly basis.
What does "months (approx)" mean?
The approximate months value is calculated as the absolute difference in calendar months between the two dates: |((year2 - year1) × 12 + (month2 - month1))|. This gives the number of complete calendar months between the dates, ignoring the day component. It is labeled "approx" because a calendar month is not a fixed number of days.
Can I calculate how many days ago a past date was?
Yes. In "Date Difference" mode, set the past date as the start date and today as the end date. The result will show a positive number of days. Alternatively, set today as the start and the past date as the end — the signed day count will be negative, and the absolute day count will be positive.
How does the tool handle date inputs?
Date inputs use the HTML date input type (format: YYYY-MM-DD). All dates are parsed as midnight local time (T00:00:00) to ensure consistent day-boundary calculations regardless of your timezone. The tool avoids UTC conversion issues by anchoring all comparisons to midnight local time.
Is there a limit on how far back or forward I can calculate?
The tool supports any date that JavaScript Date objects can handle, which covers years from approximately 100 AD to 275,760 AD. Practically speaking, you can calculate differences across any date range relevant to human history or planning purposes, such as centuries or millennia.