How we calculate

Every number on this site comes from a formula you can read below. The defaults are written down, you can change all of them, and each formula is checked by automated tests before any change goes live.

Rules that apply everywhere

Dates are whole calendar days in your own time zone. We count midnights, not 24-hour blocks, so daylight saving time never shifts a count. Leap days are included.
Feb 29 birthdays and anniversaries fall on Feb 28 in non-leap years.
Money is before tax, in US dollars, with no fees or inflation. Savings compound monthly with deposits at the end of each month.
Nothing is advice. The Money calculators do arithmetic on the numbers you choose. They do not recommend products, rates or decisions.
Everything runs in your browser. Your inputs are not sent to us unless you sign in and choose to save.

How we test

The math lives in plain functions with no user interface, and each one has test vectors: leap years, Feb 29 birthdays, birthdays today, overnight shifts, daylight-saving weekends, and compound interest checked against textbook values (for example $10,000 at 5% compounded monthly for 10 years = $16,470.09). If a test fails, the site does not deploy.

Time

Age calculator

Whole calendar months from your birth date to today, split into years and months, then the leftover days. A birthday on Feb 29 counts as Feb 28 in non-leap years.

Dates are counted in your own time zone.
Today counts as a completed day only once it has started.

Days alive

Days alive = today's date − your birth date, in whole calendar days. Weeks = days ÷ 7. Hours = days × 24.

Leap days are included.
Day 0 is the day you were born; tomorrow you are 1 day old.

Life in weeks

Weeks lived = whole days since birth ÷ 7, rounded down. Total weeks = life expectancy × 365.2425 ÷ 7. Weeks left = total − lived. One weekend per week.

Default life expectancy is 79 years, the US average at birth in 2024. Change it: yours depends on health, sex, income and where you live.

Sources: CDC NCHS — Mortality in the United States, 2024 (Data Brief 548) (checked September 29, 2026).

Age in hours

Hours = whole days since birth × 24. Minutes = hours × 60. Asleep ≈ hours × (sleep hours per day ÷ 24).

Counts whole days, so it does not need your birth time.
Sleep defaults to 8 hours a day; adults need 7 or more per the CDC, children more. Change it.

Sources: CDC — How much sleep do I need?.

Birthday countdown

Days until = next birthday date − today. If today is your birthday, the answer is 0.

Feb 29 birthdays fall on Feb 28 in non-leap years.

Days between dates

Days = end − start in calendar days (+1 if the end date is included). Workdays = Monday–Friday dates in that span. Public holidays are not removed.

Public holidays differ by country, state and employer, so they are not subtracted.

Love

Days together

Together / married: day number = today − start date + 1 (your first day is day 1). Broke up / divorced / no contact: days since = today − end date.

Milestone dates are computed in your local calendar.
Names are optional and stay on your device.

Work

Work hours

Shift = end − start − unpaid break. An end time at or before the start is the next day (overnight). Week = sum of worked days. Decimal hours = minutes ÷ 60.

Overtime rules differ by state and contract; the total is shown, overtime pay is not computed.

Hourly ⇄ salary

Yearly = hourly × hours per week × weeks per year. Monthly = yearly ÷ 12. Biweekly = yearly ÷ 26. Weekly = hourly × hours per week. Hourly = yearly ÷ (hours per week × weeks per year).

Pay before tax.
52 paid weeks a year by default: paid vacation counts as paid time.

Sources: US Department of Labor — Federal minimum wage ($7.25 since July 24, 2009); US OPM — Computing hourly rates of pay using the 2,087-hour divisor (checked September 29, 2026).

Real hourly rate

Real rate = (yearly pay − work costs per month × 12) ÷ ((hours per week + commute hours per week + unpaid hours per week) × 52).

Pay before tax, so the result compares like with like against your paper rate.
Commute is door to door, both directions, per workday.

Sources: US Census Bureau — American Community Survey, travel time to work.

Commute time

Hours per year = one-way minutes × 2 × commute days per week × commute weeks per year ÷ 60. Lifetime = hours per year × years.

48 commute weeks a year by default (4 weeks of vacation and holidays).

Sources: US Census Bureau — American Community Survey, travel time to work.

Money

Savings goal

Monthly deposit = (goal − starting amount × (1 + r)ⁿ) × r ÷ ((1 + r)ⁿ − 1), where r = yearly rate ÷ 12 and n = months. With r = 0: (goal − start) ÷ months.

Interest compounds monthly; deposits land at the end of each month.
The rate is your assumption. Savings rates change and investments can lose value.
Inflation and taxes are not included.

Sources: Investor.gov (SEC) — Compound interest calculator and glossary.

Compound growth

Balance after n months = P × (1 + r)ⁿ + monthly × ((1 + r)ⁿ − 1) ÷ r, with r = yearly rate ÷ 12. Interest = balance − everything you put in.

Monthly compounding, deposits at the end of each month.
A constant rate. Real returns vary year to year and can be negative.
No taxes, fees or inflation.

Sources: Investor.gov (SEC) — Compound interest calculator and glossary.

Found a mistake?

Tell us through the contact page with the inputs you used. We fix math errors first, add a test so it can't come back, and note the fix on the page. More about who we are and why we built this on the about page.