How many seconds are in a year?

The Julian year (used in astronomy and physics) contains exactly 31,557,600 seconds (365.25 × 86,400). The calendar year of 365 days contains exactly 31,536,000 seconds. The Gregorian average year of 365.2425 days contains approximately 31,556,952 seconds. The Julian year value of 31,557,600 is the most commonly used in scientific contexts.

How do I convert seconds to years?

Divide the number of seconds by 31,557,600 (Julian year) or 31,536,000 (calendar year). For example, 63,115,200 seconds ÷ 31,557,600 = exactly 2 Julian years. For 1,000,000,000 seconds ÷ 31,557,600 ≈ 31.69 years (the 'billion-second birthday').

How old is the universe in seconds?

The universe is approximately 13.8 billion years old. Converting: 13.8 × 10⁹ years × 31,557,600 seconds/year ≈ 4.355 × 10¹⁷ seconds — approximately 435 quadrillion seconds. This gives some sense of just how many individual seconds of cosmic history have elapsed since the Big Bang.

Seconds to Years (s to yr) Converter

1 s = 3.16881 × 10⁻⁸ yr

1 Second equals 3.16881 × 10⁻⁸ Years (1 s = 3.16881 × 10⁻⁸ yr). Convert Seconds to Years with formula, table, and examples.

One year contains approximately 31,557,600 seconds (Julian year: 365.25 × 86,400) or 31,536,000 seconds (flat 365-day calendar year). This converter uses 31,557,600 — the Julian year value most commonly used in astronomy and physics — to convert seconds to years by division. This conversion spans the extreme ends of the common time unit scale and is primarily needed in physics, astronomy, geoscience, and computing. In physics, the second is the SI base unit and all fundamental calculations use it, but results are interpreted in years when the timescale warrants it. A radioactive isotope with a half-life of 220,752,000 seconds has a half-life of exactly 7 years. In astronomy, the light-year is defined using the Julian year of 31,557,600 seconds: light travels 299,792,458 metres per second, so one light-year equals 299,792,458 × 31,557,600 = 9,460,730,472,580.8 metres. Every light-year calculation depends on the 31,557,600-second year. In computing, Unix timestamps count seconds since January 1, 1970. Dividing any Unix timestamp by 31,557,600 gives the number of years elapsed since the Unix epoch. A Unix timestamp of 1,745,280,000 (approximately the value in April 2026) divided by 31,557,600 gives approximately 55.3 years — confirming we are roughly 55 years after 1970.

How to Convert Seconds to Years

yr = s ÷ 31,557,600

Divide the value in Seconds by 31,557,600

Take your value in Seconds
Divide by 31,557,600
Read the result in Years

Common Seconds to Years Conversions

Seconds (s)	Years (yr)	Status
31,536,000 s	0.9993 yr
31,557,600 s	1 yr
63,115,200 s	2 yr
157,788,000 s	5 yr
315,576,000 s	10 yr
631,152,000 s	20 yr
946,728,000 s	30 yr
1,577,880,000 s	50 yr
2,524,608,000 s	80 yr
3,155,760,000 s	100 yr
4.355 × 10¹⁵ s	138,001,622.4301 yr

Good to Know About Seconds to Years Conversion

31,557,600 is the astronomer's year-in-seconds — the Julian year that defines the light-year and appears in astrophysical formulae worldwide. It is the companion constant to 86,400 (day), 604,800 (week), and 31,536,000 (calendar year), forming the set of second-derived year constants that appear in scientific literature across disciplines. The choice between 31,536,000 and 31,557,600 is a small but meaningful precision decision in any long-term scientific calculation.

Seconds to Years: What You Need to Know

The seconds-to-years conversion is used in radiometric dating, where the age of materials is calculated from the ratio of parent to daughter isotopes and the known decay constant in units of per second. The age comes out in seconds and is then converted to years for publication. Carbon-14 dating produces ages in the thousands of years; uranium-lead dating produces ages in millions to billions of years — always derived from second-level decay constants multiplied by 31,557,600 to get years. In climate science, ice core and sediment records are dated in years by counting annual layers, but the physical measurement of isotope ratios and gas concentrations is calibrated in seconds per sample interval. Converting between the second-level instrumental data and the year-level geological timeline is a constant operation in paleoclimatology. In astrophysics, stellar evolution models calculate how long stars spend in each phase of their life cycle. A star like the Sun spends approximately 10 billion years on the main sequence — 3.1557 × 10¹⁷ seconds. Converting observed second-level changes in stellar brightness and spectral properties to year-scale evolutionary timescales is fundamental to understanding stellar populations. In cryptography and security, password hash functions and key derivation functions are designed to take a specific number of seconds to compute, in order to slow brute-force attacks. A function taking 0.1 seconds per guess means an attacker attempting 10^12 guesses will need 10^11 seconds — approximately 3,170 years — to exhaust the key space. This conversion underlies the security analysis of every modern authentication system.

What is a Second? s

The SI base unit of time, defined by the radiation frequency of the caesium-133 atom. Used universally in science, engineering, and everyday timekeeping.

Metric SI Imperial US customary scientific measurement sports timing computing and networking

Learn more about Second →

What is a Year? yr

365.2425 days or 31,557,600 seconds, based on the Gregorian average year. The fundamental unit for expressing age, history, and long-term planning.

Gregorian calendar Civil SI accepted age and lifespan historical dates financial planning and investment

Learn more about Year →

Going the other way? Use our Years to Seconds converter.

Seconds to Years FAQ

The Julian year (used in astronomy and physics) contains exactly 31,557,600 seconds (365.25 × 86,400). The calendar year of 365 days contains exactly 31,536,000 seconds. The Gregorian average year of 365.2425 days contains approximately 31,556,952 seconds. The Julian year value of 31,557,600 is the most commonly used in scientific contexts.
Divide the number of seconds by 31,557,600 (Julian year) or 31,536,000 (calendar year). For example, 63,115,200 seconds ÷ 31,557,600 = exactly 2 Julian years. For 1,000,000,000 seconds ÷ 31,557,600 ≈ 31.69 years (the 'billion-second birthday').
The universe is approximately 13.8 billion years old. Converting: 13.8 × 10⁹ years × 31,557,600 seconds/year ≈ 4.355 × 10¹⁷ seconds — approximately 435 quadrillion seconds. This gives some sense of just how many individual seconds of cosmic history have elapsed since the Big Bang.

Non-Frequently Asked Questions About Seconds to Years

Questions nobody should ask - but someone did.

122 years × 31,557,600 ≈ 3,850,027,200 seconds — nearly 3.85 billion seconds. Jeanne Calment, who lived from 1875 to 1997, accumulated more seconds of life than almost any human in recorded history. She was born before the invention of the telephone and died having used the internet. The seconds-to-years conversion makes her longevity suitably enormous.
£1,000,000,000 ÷ 1 = 1,000,000,000 seconds. Divided by 31,557,600, that is approximately 31.69 years of earning £1 every second, day and night, without spending any of it. At the UK median salary of roughly £35,000 per year, reaching £1 billion would take approximately 28,571 years. The seconds-to-years conversion is a useful tool for calibrating intuitions about large numbers and wealth.
100,000,000 seconds ÷ 31,557,600 ≈ 3.17 years. A wine that has aged for 100 million seconds is approximately a 2022 vintage if bottled today in 2026 — a decent young table wine but nothing that commands serious cellar space. To age for a century (100 years), a wine would need 3,155,760,000 seconds, which is also approximately the age of the oldest surviving written recipes.