Date Calculator

What this date calculator does

This English-language date calculator handles two everyday tasks: finding the exact number of days between two dates, and shifting a date forward or backward by a given number of days. All arithmetic runs in UTC, so a calculation that crosses a daylight-saving boundary in America/New_York — or anywhere else — won't silently drop or gain a day the way new Date(d1) - new Date(d2) // ms can in local time. The difference mode returns total days, total weeks, total months, total years, and a full years/months/days calendar breakdown. The add/subtract mode accepts negative values to go back in time. Everything runs 100% client-side — your data never leaves your browser. No uploads, no tracking, no server logs. The Stack Overflow Developer Survey 2024 lists ISO 8601 as developers' most preferred date format, and this tool treats all inputs as ISO 8601 date-only values, so results are unambiguous regardless of locale.

Features

• Days between two dates. Enter any start and end date to get the total count — useful as a day counter, days calculator, or calendar calculator for deadlines, lease terms, and schedules.
• Full calendar breakdown. Beyond a raw day count, you get a years/months/days decomposition — the same format courts and HR teams use for tenure or notice-period calculations.
• All four total-unit conversions. Total days, total weeks, total months, and total years appear side by side so you can pick the unit that fits your context without doing secondary math.
• Add or subtract days. Pick a base date, enter a positive or negative integer, and get the resulting date instantly — no need to count forward on a calendar or reach for from datetime import date; (date(2030,1,1)-date.today()).days in a terminal.
• UTC-only arithmetic. Date-only inputs are evaluated in UTC, eliminating the off-by-one errors that trip up local-time solutions when a DST transition falls inside the range. If you need to go deeper into timestamps, the [Unix timestamp converter](/en/timestamp-converter/) handles epoch values.
• Correct leap-year handling. The calculator applies the full Gregorian rule: divisible by 4 is a leap year, except century years — unless divisible by 400. So 1900 was not a leap year, but 2000 was.

How to use the date calculator

Pick a mode, fill in the date fields, and the result updates immediately — no form submission needed.

1. Choose a mode. Select "Difference between dates" to count the gap between two calendar dates, or "Add / subtract days" to shift a single date by a number of days.
2. Enter your dates. Type dates in YYYY-MM-DD format (ISO 8601) or use the date picker. For the add/subtract mode, enter the number of days — negative values subtract.
3. Read the result. The result section shows total days, weeks, months, and years. In difference mode, the calendar breakdown gives you the years/months/days split — handy for contract or visa duration questions.
4. Verify edge cases. If your range spans February 29, the leap-year rule is applied automatically. For business-days needs, remember the tool counts calendar days; working days require holiday data not available here — see your HR system or a working days calculator for that.

Common use cases

• Contract and notice periods. Employment contracts, lease agreements, and supplier terms all specify durations in days or months. Use the days-between mode to verify a 90-day notice period or a 12-month lease end date — and watch the inclusive/exclusive end-date convention, since some contracts count the last day and others do not.
• Project deadline planning. Drop your launch date into the add/subtract mode and count back to set milestones. A team in Dublin planning a 45-day sprint can confirm the end date without opening a spreadsheet.
• Visa, subscription, and warranty windows. Many visa categories grant exactly 90 days of stay. Calculate your entry date plus 90 days to find the last legal day — critical when overstays carry fines or future entry bans.
• Age and milestone math. Need to calculate time from a date of birth to today, or compute age at a specific point? The calendar breakdown handles that. For a dedicated age result with birthday formatting, the [age calculator](/en/age-calculator/) goes further.
• Anniversary and due-date tracking. Confirm how many days remain until an anniversary, a product ship date, or a medical follow-up. The day counter updates in real time as you adjust either date.

Frequently asked questions