Some people love to confuse “Reformed” as a historical family of churches with “reformed” as a broader theological tradition. The short answer: Reformed Baptists are indeed Reformed in theology, though not confessionally identical to the continental or Presbyterian Reformed churches. The fact that they are credobaptist does not automatically make them non-Reformed in every meaningful sense.
Now, let’s distinguish categories, otherwise it’s like me trying to work with dull scissors.
Historically: “Reformed” can mean a confessional church family. In the strict historical-confessional sense, “Reformed” traditionally refers to churches standing in the line of: The Three Forms of Unity (Belgic Confession, Heidelberg Catechism, Canons of Dort) or the Westminster Standards.
These churches are classically paedobaptist and covenantal in a particular way. By this narrower definition, some Presbyterians and continental Reformed folk will say: “Reformed Baptists are not Reformed because they reject infant baptism.” What they usually mean is: “They are not part of the classical magisterial Reformed confessional tradition.”
That is a historically coherent statement.
Theologically: Reformed Baptists are plainly Reformed in doctrine. Now in the broader theological sense, Reformed Baptists , especially those holding the 1689 London Baptist Confession , absolutely stand within the Reformed stream. They affirm: Sola Scriptura, Sola Fide, Sola Gratia, Solus Christus, Soli Deo Gloria … the doctrines of grace (TULIP), covenant theology (though distinct from Westminster), God’s absolute sovereignty in salvation, justification by faith alone, perseverance of the saints. In other words, on the doctrines most people mean by “Calvinism,” they are thoroughly Reformed.
The 1689 itself is heavily indebted to Westminster and Savoy, so much so that anyone denying its Reformed pedigree must first explain why it looks so much like Westminster. Baptism is the point of divergence, not the whole system. This is the major point of separation – sacramentology and covenant administration.
The 1689 Federalists differ especially on: who receives baptism, the relation of the New Covenant to the Abrahamic covenant, the visible church. That is significant, yes. But one doctrinal disagreement does not erase the rest of the theological architecture. Otherwise, by that absurd logic, Lutherans would cease to be Protestant because they differ from the Reformed on the Lord’s Supper.
A better way to say it is Reformed Baptists are confessionally Baptist and theologically Reformed. Or if someone wants more precision: They belong to the Particular Baptist tradition within the broader Reformed/Calvinistic theological heritage. That avoids the silly tribal posturing.
Frankly, too many people (especially Presbyterians) use the word “Reformed” less as a theological descriptor and more as a club badge. One must not confuse denominational boundary markers with doctrinal substance.
Let me be more blunt: if a man confesses the sovereignty of God in salvation, justification by faith alone, the authority of Scripture, and subscribes to the 1689, it is rather strained to pretend he has wandered off into theological Arminianism merely because he will not sprinkle infants. So yes , Reformed Baptists are legitimately called Reformed in the broader theological sense, while in the narrow (minded) confessional-historical sense some reserve the term for paedobaptist traditions. Both uses exist. The quarrel is usually about definitions, not substance.
If you prefer wet babies, fine. I’m still Reformed. And Baptist. And in the same camp as Charles Haddon Spurgeon. Not bad company.