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Convert Seconds to Years - Time Converter

This converter transforms a single input value expressed in seconds into the equivalent number of years. The calculator uses the internationally recognised SI second as the base time unit and expresses results according to a chosen reference year length.

Because the length of a "year" can be defined in several valid ways (calendar year, average Gregorian year, Julian year, or an exact 365-day year), this page explains the default choice, the commonly used alternatives, and the accuracy implications for different use cases.

Updated Nov 30, 2025

Interactive Converter

Convert between second and year with precision rounding.

Quick reference table

SecondYear
1 s0 yr
5 s0 yr
10 s0 yr
25 s0.000001 yr
50 s0.000002 yr
100 s0.000003 yr

Methodology

Base unit: the second is the SI base unit for time. For traceability and high-precision work follow the SI second definition as maintained by national metrology institutes.

Reference year: this converter uses the average Gregorian calendar year (365.2425 days = 31,556,952 seconds) as the default reference for a civil year. This average accounts for leap years in the Gregorian calendar and is appropriate for most civil and planning purposes.

Alternative definitions: the Julian year (365.25 days = 31,557,600 seconds) and the exact 365-day year (31,536,000 seconds) are provided as documented alternatives because some scientific fields and legacy systems use those conventions. For high-precision timing (sub-second per year), account for leap seconds and use specialized timekeeping standards and protocols.

Worked examples

1,000,000,000 seconds ≈ 31.6880878 years (using default Gregorian mean year: 1,000,000,000 / 31,556,952 ≈ 31.688088).

31,557,600 seconds = 1.000008 years (Julian year reference).

31,536,000 seconds = 1.000000 years (exact 365-day year reference).

Expert Q&A

Which definition of year does this converter use by default?

By default it uses the average Gregorian calendar year (365.2425 days = 31,556,952 seconds), which aligns with civil calendar conventions and is suitable for most planning and reporting tasks.

Why are there different answers for the same number of seconds?

Different fields use different year definitions (calendar average, Julian, exact 365-day). Each definition yields a slightly different seconds-per-year value; pick the definition that matches your context.

Do leap seconds affect the conversion?

Leap seconds alter the relationship between UTC and astronomical time scales. For conversions intended for civil timescales over years, using an average year length is acceptable. For high-precision timekeeping (e.g., synchronization, timestamps, or metrology) account for leap seconds and use standards and protocols designed for that purpose.

How precise is the result?

The mathematical division is exact to the precision of your input and display. Practical accuracy depends on the chosen year definition and whether leap seconds or relativistic/time-scale corrections are relevant to your use case.

Can I convert back from years to seconds?

Yes. Multiply the number of years by the same reference year length in seconds that you used for the forward conversion.

Sources & citations