Acts 18:21

But as he left, he said, “I will come back to you if God is willing.” And he set sail from Ephesus.

Scripture: Berean Standard Bible (BSB), public domain

ON THE MAP

WHEN

c. AD 49-52

counted from the text

The eighteen months in Corinth fit Paul into the Roman calendar in years, not just in order.

WHO RULED

MEANWHILE

c. AD 49 Italy

Claudius expels the Jews from Rome

That is why Aquila and Priscilla are in Corinth when Paul arrives, in Acts 18:2.
AD 51-52 Achaia

Gallio is proconsul of Achaia

The Delphi inscription dates his term, and with it the only fixed date in Paul's life.

SOURCES

date — Acts 18:12 puts Paul before Gallio, proconsul of Achaia in AD 51-52 by the Delphi inscription. It is the anchor of the whole chronology of Paul.
Claudius — Suetonius, Claudius; Tacitus, Annals XI-XII
Gallio — Delphi inscription (SIG 801d), which dates his term; Acts 18:12. It is the only fixed date in Paul's chronology.
Herod Agrippa II — Josephus, Jewish War II; Antiquities XX
Antonius Felix — Josephus, Antiquities XX.7-8; Tacitus, Annals XII.54
Claudius expels the Jews from Rome — Suetonius, Claudius 25.4; Orosius VII.6
Gallio is proconsul of Achaia — Delphi inscription (SIG 801d); Acts 18:12