Date & Time

Age calculator, date difference, time zone, and business days calculators.

A

Age Calculator

Calculate exact age in years, months, and days. See total days lived, next birthday countdown, and zodiac sign.
D

Date Calculator

Calculate days between two dates or add/subtract days from a date. Shows business days excluding weekends.
T

Time Zone Converter

Convert time between US and international time zones instantly.
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Time Duration Calculator

Calculate hours and minutes between two times with overnight support.
B

Business Days Calculator

Count business days between dates excluding weekends and estimated holidays.
C

Countdown Calculator

Calculate days, weeks, and months until a target date.
W

Week Number Calculator

Find the ISO week number, day of year, and quarter for any date.

About Date & Time Calculators

Date and time math looks trivial until a deadline, a benefit eligibility date, or a paycheck depends on getting it exactly right. The seven tools here turn calendar arithmetic into decisions you can act on. The Age Calculator pins down the dates that trigger federal milestones, your Medicare enrollment window at 65, Social Security full retirement age as defined by the SSA, and the year required minimum distributions begin (age 73 under current IRS rules).

Timing the rest of the calendar matters just as much. The Date Calculator counts the exact days between two dates for statute-of-limitations windows, USCIS continuous-residence requirements, or court filing deadlines. The Business Days Calculator skips weekends and federal holidays, which is how the IRS decides when a due date rolls to the next business day and how banks estimate ACH and check clearing. The Time Zone Converter keeps you on the right side of a midnight e-file or market cutoff, while the Time Duration Calculator handles FLSA timesheet math down to the minute.

Reach for these whenever a date carries consequences: open enrollment, a tax due date, or the 401(k) catch-up that becomes available the year you turn 50.

Frequently Asked Questions

How do I count business days for an IRS or court deadline?
Business days exclude Saturdays, Sundays, and federal holidays recognized by the Office of Personnel Management, such as New Year's Day, Independence Day, Thanksgiving, and Christmas. The IRS applies a specific rule: when a filing or payment deadline lands on a weekend or legal holiday, it moves to the next business day. State courts and agencies often follow similar conventions, but each sets its own holiday calendar, so confirm with the specific court or agency.
What age do I become eligible for Social Security and Medicare?
You can claim Social Security retirement benefits as early as age 62, but your full retirement age is 66 to 67 depending on your birth year, as set by the Social Security Administration, and waiting past it increases your monthly benefit. Medicare eligibility begins at 65 for most people, with a seven-month Initial Enrollment Period that starts three months before your 65th birthday month. Knowing the exact calendar dates helps you avoid late-enrollment penalties administered by CMS.
Does the time zone matter for filing taxes or meeting an online deadline?
Yes. Most federal deadlines, including IRS e-file cutoffs, are based on the timezone where the deadline is defined, and an electronic submission is generally considered timely if transmitted before midnight in your local time zone. For court e-filing, brokerage trades, and benefit applications, the controlling time zone can differ from yours. When you are filing close to a cutoff, convert the deadline to your local time first so a few hours' difference doesn't make a same-day filing late.
How are weeks and pay periods numbered during the year?
The ISO 8601 standard numbers weeks 1 through 52 or 53, with week 1 being the week containing the year's first Thursday and weeks starting on Monday. U.S. payroll and accounting systems often use this for fiscal reporting, though some employers number weeks from January 1 or align them to their own fiscal calendar. Because a year can hold 53 ISO weeks, biweekly payrolls occasionally produce a 27th pay period, which affects per-paycheck withholding.
When does my age change my retirement contribution or distribution rules?
Several IRS thresholds are tied to specific ages. Starting the year you turn 50, you can make catch-up contributions on top of the standard 401(k) employee deferral limit of $24,500. Required minimum distributions from traditional 401(k)s and IRAs generally begin at age 73 under current law, and missing the deadline can trigger an excise tax. Pinning down the exact calendar year you cross each age helps you act in the right tax year.