The phrase "how many years" is generally used to inquire about the number of years between two dates, the duration of time in years, or the age of something or someone. A year is defined as the time it takes for the Earth to complete one orbit around the Sun, approximately 365.25 days. To calculate how many years are between two dates, you find the number of days between those dates (including leap years if applicable) and then divide by 365.25 to account for the quarter day in each year. Calculators are available that can give precise results including years, months, and days between two dates. If a specific calculation or context is intended, providing the two dates or time frames would allow calculation of the exact number of years.