Time & Date Calculators: Date Calculator, Hours, Age & More

Days Between Two Dates From a Start Date to an End Date

A date difference is the count of days from your start date to your end date. A days between dates calculator turns each date into a time stamp, subtracts one from the other and converts the elapsed time back into days and years. That's why a date difference calculator never trips over month lengths the way a hand count does.

Two settings change the answer:

• Include end day adds 1 day, so the last day itself counts. Use it for hotel stays you pay per night only if you also count checkout, or for leave that covers both dates.
• Business days drops Saturdays, Sundays and, if you choose, public holidays.

Take 14 January 2027 to 9 August 2027. The days calculator returns 207 days, or 208 with the end day included. Counting only weekdays gives 147, and removing five public holidays in that window leaves 142.

Weeks Between Dates and Remainder Days

To find the weeks between dates, divide the day count by 7:

$$\text{weeks} = \frac{\text{days}}{7}$$

1. Count the days: 207.
2. Divide by 7: \(207 \div 7 = 29.5714\), so 29 whole weeks.
3. Multiply the fraction after the point by 7 to get the remainder days: \(0.5714 \times 7 = 4\).

The answer is 29 weeks and 4 days, the format most people actually want for a pregnancy, a notice period or a training plan.

Add to or Subtract From a Date With a Date Calculator

The other half of date math runs the opposite way: you know the start and the length, and you need the end. A date calculator lets you add or subtract days, weeks, months, quarters or years, which is what a date ± calendar units tool does. Start on 18 November 2026, add 100 days and you land on Friday, 26 February 2027. Subtract 6 weeks instead and you get 7 October 2026.

Related tools cover the same need from other angles:

• Days from today and days until counters for a launch, exam or trip.
• A countdown timer that ticks down to an event in real time; a countdown is handy for project and schedule planning.
• A business days calculator that skips weekends when a contract says "within 30 working days."
• A day of the week calculator that tells you whether a date falls on a Monday or a Sunday, past or future.

Age Calculator: How Old You Are in Days

An age calculator is a day count with your date of birth as the first date and today as the end. Someone born on 3 May 1991 is 12,946 days old on 12 October 2026, which is 35 years and change. The same math tells you how old a building is, how many days until your next birthday or anniversary, or how long until you retire. Some tools go further and break your age down to the minute.

Checking an Invoice Due Date With a Business Days Calculator

I'm a freelance bookkeeper with a $4,862.50 invoice dated Thursday, 15 October 2026, and the client's contract says payment is due "within 30 business days of the invoice date, excluding US federal holidays." I want one thing: the first day I can charge the 1.5% late fee without starting an argument. The answer is Monday, 30 November 2026.

Here's how I get there. I enter 15 October as the start date, choose "add" and type 30, then switch the count to business days. With weekends removed and no holidays ticked, the date calculator lands on Thursday, 26 November. That date is Thanksgiving, which is a warning sign, so I turn on federal holidays. Two fall in the window, Veterans Day (Wed, 11 November) and Thanksgiving (26 November), and each one pushes the deadline back a working day:

I cross-check by hand: 15 October to 30 November is 46 days, which is 6 full weeks plus 4 days. Six weeks hold 30 weekdays and the 4 extra days (Friday to Monday) add 2 more, so 32 weekdays, minus the 2 holidays, gives exactly 30.

What stands out is how far a "30-day" term stretches. Switch the count back to calendar days and the calculator gives Saturday, 14 November, the rule the US Prompt Payment Act uses for federal agencies and 16 days earlier than the business-day answer. The caveat that matters most is the start trigger: many clients count from the day they receive the invoice, not the date printed on it. If this one arrived on Monday, 19 October, I rerun with that start date and the due date moves to 2 December. Black Friday is not a federal holiday, but plenty of offices close, so I add it as a custom holiday, which gives 1 December, and I treat that as the safe date.

My next step is concrete: I put a 1 December reminder in the calendar and rewrite my own contract so it says "30 calendar days from the invoice date," which removes the guesswork for both sides.

Time Calculators for Work Hours, Breaks and Time Card Totals

Time calculators handle the clock rather than the calendar. An hours calculator finds a single time span, while a time card tool totals a whole work week, subtracts breaks and feeds payroll. Say a shift runs from 8:40 am to 5:25 pm with a 35-minute unpaid break:

$$8\text{h}\,45\text{m} - 35\text{m} = 8\text{h}\,10\text{m} = 8.1667 \text{ hours}$$

At $23.40 an hour, that's $191.10 gross pay before taxes. Employees and managers use these totals for time tracking and to check that work hours on a pay slip add up.

Other tools in this group:

• A time calculator that adds, subtracts, multiplies and divides days, hours, minutes and seconds.
• An hh:mm:ss adder for cumulative time across many entries.
• A stopwatch lap time adder that works in hundredths of a second.
• A sunrise and sunset finder for any latitude and longitude.

Time Conversions: Decimal Hours and Military Time

Payroll systems want decimal hours, not clock time. Divide the minutes by 60: \(\text{decimal} = \text{minutes} \div 60\). A time units converter does the same for seconds and days, and a military time converter switches 5:25 pm to 1725.

Time & Date Calculators and the Gregorian Calendar

Every day count above depends on the Gregorian calendar, and its rules are what the calculators apply each time they count a gap. It replaced the Julian calendar, which Julius Caesar introduced in 46 BC to fix a drifting lunar Roman calendar patched with intercalary months. The Julian year of 365 days plus a leap day every fourth year ran about 11 minutes longer than the solar year, so the equinoxes drifted until, in 1582, Pope Gregory XIII skipped 10 days and changed the leap year rule:

• A year divisible by 4 is a leap year and February gets 29 days.
• Century years are not leap years unless they are also divisible by 400, so 2000 was one and 2100 won't be.

So 1 February to 1 March is 29 days in 2028 but only 28 in 2100, and a calculator gets both right.

Month lengths are the other trap. The old mnemonic still works:

Thirty days have September, April, June and November; all the rest have 31, except February alone.

That's why Time & Date Calculators beat mental math: they apply the leap-year and month-length rules for you on every count, so none of that history has to live in your head.

How Federal Holidays Change Business Days Counts

Holidays are days set aside by law or custom when work stops. In the US, federal holidays close non-essential government offices and give federal staff paid leave; private employers choose which ones to honor, and many count them separately from vacation. Some are fixed holidays, such as New Year's Day on January 1. Others float: Martin Luther King Jr. Day falls on a floating Monday, the third Monday of January, and Thanksgiving is the fourth Thursday of November. When a fixed date lands on a weekend, the day off moves.

A business day count that skips holidays should use the observed dates, not the calendar dates.