The 0s (1–9 AD): the first years after Christ and the absence of year zero

Overview of the decade called the 0s, why the Anno Domini system lacks a year zero, how that affects counting decades and centuries, and the alternative astronomical numbering that includes year 0.

The phrase "the 0s" is ambiguous because the traditional Anno Domini (AD) calendar system used in much of the world contains no year zero. In that scheme the sequence runs 1 BC, AD 1, AD 2, and so on. As a result, what might be called the "0s" in ordinary numeric terms — years labelled 0 through 9 — does not exist in the historical AD/BC numbering. Instead the earliest span commonly referred to as the 0s comprises nine calendar years, AD 1 through AD 9.

Why there is no year zero

The lack of a year zero stems from how the AD system was devised during the early medieval period. The monk Dionysius Exiguus is credited with introducing Anno Domini dating in the sixth century; he and other medieval writers treated years as ordinal counts that begin with 1, so the era before and after the calculated birth of Christ are adjacent without an intervening zero year. Ancient Roman and medieval number systems generally did not use a concept of zero in counting years, and later calendar reforms (including the Gregorian reform) altered leap rules and dates but not the basic ordinal numbering that omits year zero.

Counting, ambiguity, and modern alternatives

Because everyday labels such as "the 1900s" or "the 0s" can mean either a set of years sharing a digit pattern or a ten‑year block beginning with a year ending in 0, ambiguity arises. Around the birth of the Christian era the ambiguity is pronounced: there is no AD 0, so a literal 0–9 set would be nine years rather than ten. To avoid confusion, historians often write explicit ranges (for example, "AD 1–9" or "the first decade AD") or use "early first century".

Astronomical year numbering and ISO 8601 include a year 0, equivalent to 1 BC in the traditional scheme, and use negative numbers for earlier years; this system is convenient for calculation.
BCE/CE notation keeps the same numbering as BC/AD, so it does not introduce a year zero unless astronomical or ISO conventions are specified.
Practical consequences include occasional off‑by‑one errors when computing intervals that cross the BC/AD boundary and recurring public debates over when centuries and millennia begin.

In sum, "the 0s" in the historical AD system refers informally to the first nine years after AD 1. Being explicit about whether one uses historical AD/BC numbering or astronomical/ISO year numbering (which has a year 0) prevents misunderstanding when discussing dates that span eras.