Age Calculator

How age is calculated

This calculator counts complete years between your birth date and today, then complete months since your last birthday, then the remaining days — the same way you'd count on a calendar by hand. Month-length differences (like a January 31st birthday compared against February) are handled by clamping to the end of the shorter month, matching how most calendar tools resolve that ambiguity.

Worked example: someone born May 15, 1990 is 36 years, 2 months and 8 days old on July 23, 2026. That's 36 birthdays (the last on May 15, 2026), two more month-steps to July 15, then 8 days. In total it's 13,218 days, about 1,888 weeks. To count days between any two dates, or add days to a date, use the date calculator; for hours and minutes, the hours calculator.

Dog years to human years

A dog's first year of life is roughly equivalent to 15 human years, and the second year adds about 9 more (24 total at 2 dog years) — dogs mature much faster than humans early on. After that, each additional dog year adds roughly 4 to 5.5 human years depending on size, since larger breeds tend to age faster in their later years than smaller ones. This calculator uses that size-adjusted rate rather than the old flat "multiply by 7" rule of thumb, which isn't accurate for most of a dog's life.

Social Security retirement age

US Social Security defines three key ages: 62 for early retirement (with permanently reduced benefits), 65 for Medicare eligibility, and a "full retirement age" for unreduced benefits that depends on your birth year — 65 for anyone born in 1937 or earlier, rising in two-month steps through the mid-1950s, and settling at 67 for anyone born in 1960 or later. This calculator computes all three and the dates they apply from.

A few SSA rules shift those dates, and the calculator applies them:

• You reach an age the day before your birthday. SSA follows this common-law rule, so a January 1 birthday is read with the previous year's full retirement age: someone born January 1, 1960 has a full retirement age of 66 and 10 months, not 67.
• Early benefits need a full month at 62. You must be 62 for the whole month, so the first month you can be paid for is usually the month after your 62nd birthday. If you were born on the 1st or 2nd, it's your birthday month. Benefits are paid the following month.
• Medicare starts on the 1st of your 65th-birthday month for premium-free Part A, or the month before if your birthday is on the 1st. Part B start dates depend on when you sign up.

Claiming early permanently reduces the monthly benefit: by 5/9 of 1% for each of the first 36 months before full retirement age and 5/12 of 1% for each month beyond that. With a full retirement age of 67, claiming at 62 is 60 months early, a reduction of about 30%. The calculator shows ages and dates only; your benefit amount comes from your my Social Security account at ssa.gov.

Full retirement age by birth year

The table below is the SSA schedule the calculator uses. If you were born on January 1, use the row for the year before.

"Biological" vs. chronological age

Chronological age is simply time elapsed since birth — what this calculator reports, and the number used for legal and administrative purposes. "Biological age" is a separate, more involved estimate of how old your body functions based on measurable biomarkers, and it requires bloodwork, a DNA test, or a clinical assessment to calculate — no calculator can derive it from a birth date alone. Different tests use different markers, so two biological-age results for the same person often disagree.

Sources

The formulas on this page come from the published research below. Last updated October 11, 2026. This calculator gives estimates for general information. It isn't medical advice, so check anything important with a qualified professional.

1. U.S. Social Security Administration. Benefits Planner: Retirement Age Calculator.Used for: Full retirement age by birth year, including the rule that a January 1 birthday uses the previous year
2. U.S. Social Security Administration. POMS RS 00615.004 — Attainment of Age.Used for: When early (age 62) retirement eligibility begins
3. Medicare.gov. When does Medicare coverage start?Used for: Medicare start date at 65