|Millennium:||1st millennium BC|
|28 BC by topic|
|Gregorian calendar||28 BC|
|Ab urbe condita||726|
|Ancient Greek era||188th Olympiad (victor)¹|
|Balinese saka calendar||N/A|
|Chinese calendar||壬辰年 (Water Dragon)|
2669 or 2609
— to —
癸巳年 (Water Snake)
2670 or 2610
|Coptic calendar||−311 – −310|
|Ethiopian calendar||−35 – −34|
|- Vikram Samvat||29–30|
|- Shaka Samvat||N/A|
|- Kali Yuga||3073–3074|
|Iranian calendar||649 BP – 648 BP|
|Islamic calendar||669 BH – 668 BH|
|Julian calendar||28 BC|
|Minguo calendar||1939 before ROC|
|Seleucid era||284/285 AG|
|Thai solar calendar||515–516|
99 or −282 or −1054
— to —
100 or −281 or −1053
Year 28 BC was either a common year starting on Saturday, Sunday or Monday or a leap year starting on Saturday or Sunday (link will display the full calendar) of the Julian calendar (the sources differ, see leap year error for further information) and a common year starting on Saturday of the Proleptic Julian calendar. At the time, it was known as the Year of the First Consulship of Octavian and Agrippa (or, less frequently, year 726 Ab urbe condita). The denomination 28 BC for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
- Gaius Julius Caesar Octavian becomes Roman Consul for the sixth time. His partner Marcus Vipsanius Agrippa becomes Consul for the second time.
- The Roman Senate granted Octavian Caesar the title imperium maius (supreme commander) of the Roman armed forces (Around 60 legions).
- Augustus initiated a census of the Roman Republic for the first time since 69 BC.
- May 10 – The earliest dated record of a sunspot by Chinese astronomers.
- The Emilius comet is said to have crashed into modern day Pakistan.