# How old will I be in a future year?

Works out how old you will be in any future year, from your date of birth or from your age now, before and after your birthday that year.

- Page: https://www.acalculator.org/days/how-old-will-i-be-calculator
- JSON spec: https://www.acalculator.org/days/how-old-will-i-be-calculator.json
- Version: f757416c4d33

## Default answer

Example with the default inputs (I know My age now, Age now 11, Birthday this year? Already had it, Today’s date October 19, 2026, In the year 2050) on the example date Monday, October 19, 2026: That year you will be 35 after your birthday, and 34 before it.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| known | I know | Your date of birth, or only your age now. |
| age | Age now | Your age today in whole years. |
| had | Birthday this year? | Whether your birthday has already come this year. |
| on | Today’s date | The date your age now is for. Today, unless you change it. |
| birth | Birth date | Your date of birth. |
| year | In the year | The future (or past) year to find your age in. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| after | Age after your birthday that year | The year minus your birth year. |
| before | Age before your birthday that year | One less than after the birthday. |
| born | Birth year | The year you were born. |

## Method

Birth year B = the year of the birth date, or this year − age now (− 1 more if this year’s birthday has not come). In year T: age after the birthday = T − B; before it = T − B − 1.

## Assumptions

- Age is counted in complete years: it goes up by 1 on each birthday and is never rounded up.
- Only the year of each date is used.

## Worked examples

1. known = age, age = 11, had = yes, on = 2026-10-18, year = 2050 gives born = 2015, after = 35, before = 34. Source: U.S. Census Bureau, American Community Survey 2023 Subject Definitions, Age: age in complete years as of the date, not rounded up before a birthday. https://www2.census.gov/programs-surveys/acs/tech_docs/subject_definitions/2023_ACSSubjectDefinitions.pdf.
2. known = age, age = 11, had = no, on = 2026-10-18, year = 2050 gives born = 2014, after = 36, before = 35. Source: U.S. Census Bureau, American Community Survey 2023 Subject Definitions, Age: age in complete years as of the date, not rounded up before a birthday. https://www2.census.gov/programs-surveys/acs/tech_docs/subject_definitions/2023_ACSSubjectDefinitions.pdf.
3. known = birth, birth = 1990-07-04, year = 2040 gives born = 1990, after = 50, before = 49. Source: U.S. Census Bureau, American Community Survey 2023 Subject Definitions, Age: age in complete years as of the date, not rounded up before a birthday. https://www2.census.gov/programs-surveys/acs/tech_docs/subject_definitions/2023_ACSSubjectDefinitions.pdf.

## FAQ

### If I am 11 now, how old will I be in 2050?

In 2026, an 11-year-old who has had this year’s birthday was born in 2015, so in 2050 they turn 2050 − 2015 = 35, and are 34 before that birthday. If the birthday is still to come in 2026, they were born in 2014 and turn 36 in 2050.

### How do I work out my age in a future year?

Subtract your birth year from that year. That is your age after your birthday in that year; before the birthday you are one year younger.

### Why are there two ages for one year?

Your age goes up on your birthday, partway through the year. Before it, you are one year younger than after it.

### How old will I be in 2030 if I was born in 2000?

2030 − 2000 = 30 after your birthday in 2030, and 29 before it.

### Does a February 29 birthday change the answer?

Not for a whole year: the age after the birthday is still the year minus the birth year. In a common year, most people with a February 29 birthday celebrate on February 28 or March 1.

## Sources

- U.S. Census Bureau, American Community Survey 2023 Subject Definitions, Age: age is the age in complete years as of the date, not rounded up before a birthday. https://www2.census.gov/programs-surveys/acs/tech_docs/subject_definitions/2023_ACSSubjectDefinitions.pdf (cited from the copy already in this repo, src/families/how-old-am-i)