Free Date Calculator Online - Calculate Date Difference, Add/Subtract & Format Dates
Calculate date differences, add or subtract days, convert between formats, and calculate age — all in real time.
How to Use Date Calculator
Select a Mode
Choose Difference to compare two dates, Add / Subtract to calculate a future or past date, Format to convert a date into different display formats, or Age to calculate your exact age from a birth date.
Enter Your Dates
Use the native date picker or type a date in YYYY-MM-DD format. Click the Today button next to any input to jump to the current date instantly.
View and Copy Results
Results update automatically as you change inputs — no need to click a Calculate button. Use the copy icon next to each result to copy that value to your clipboard.
Frequently Asked Questions
Date Difference
How do I calculate the difference between two dates?
To calculate the difference between two dates, select the "Difference" mode, then pick your start date and end date using the date pickers. The tool will instantly show you the number of days, weeks, months, and years between them. This is useful for counting days until an event, calculating tenure, or determining age. The calculation accounts for leap years and different month lengths automatically. You can also choose whether to include the end date in the difference calculation.
Can I calculate someone's age?
Yes, use the age calculator feature. Enter the birth date in the designated date picker, and the tool will instantly compute the person's age in years, months, and days based on the current date (or a custom end date if provided). This is perfect for age verification, birthday reminders, or filling out forms that require exact age. The calculation is accurate to the day and accounts for leap years.
Does it count both start and end dates?
By default, when calculating date differences, this tool counts the number of full days between the start and end dates — meaning it does not include both endpoints. For example, from Monday to Wednesday, the difference is 2 days (Tuesday and Wednesday). If you need to include the end date (e.g., for booking calculations), there is an optional "Include end date" checkbox that adds one extra day to the result. Check the box if your use case requires inclusive counting.
Add & Subtract
What is 90 days from today?
Use the Add/Subtract mode to find any date in the future or past. Enter today's date (or click the "Today" button), set the quantity to 90, select "Days" as the unit, and choose "Add" direction. The tool will instantly show you the exact date 90 days from today. This works for any number of days, weeks, months, or years. You can also subtract to find past dates, like "what date was 30 days ago?"
How do I add or subtract from a date?
Select the "Add / Subtract" tab, pick a base date using the date picker, and choose whether to add days or subtract days using the direction buttons. Then enter the quantity and select the unit — days, weeks, months, or years. The result date appears instantly along with its week day name and alternative date format representations. You can also use the "Today" shortcut button to quickly set the base date to the current date before performing any date arithmetic.
Date Formats & More
What date formats are supported?
The Format mode supports multiple popular date formats: ISO (YYYY-MM-DD), US (MM/DD/YYYY), European (DD/MM/YYYY), Long format (Month DD, YYYY), and short weekday format (e.g., "Wed, May 21, 2026"). Each format is displayed with a copy button so you can quickly paste the formatted date into your documents, spreadsheets, or code. You can also convert any date you enter into all these formats instantly.
How do I find the week number of a date?
To find the week number of a specific date, enter the date in the Format mode. The tool will display the weekday name (Monday to Sunday) and also the ISO week number if supported. Week numbers are useful for project planning, payroll cycles, academic calendars, and reporting. The ISO week numbering system follows the standard where week 1 is the week containing the first Thursday of the year.
Can I calculate business days (excluding weekends)?
This feature is planned for future updates. Currently, the calculator counts all calendar days including weekends. For business day calculations (excluding Saturdays and Sundays), you can manually adjust the result or use a dedicated workday calculator tool. Many users request this for project deadline planning — please stay tuned for an update that will include a "Business Days" mode.