Did the Reformation Legalize Interest? Luther, Calvin and Modern Usury

Ask a Christian investor why owning a bank is fine but owning a casino is not, and you will usually get some version of "Calvin settled that." The story goes that the Reformers threw out the medieval ban on lending at interest, redefined usury as excessive interest only, and cleared the runway for modern banking. It is a tidy story. It is also about half wrong, and the half that is wrong matters if you are trying to build a portfolio on biblical grounds. The primary texts tell a messier version.

The scriptural material everyone was arguing about

The Hebrew Bible uses two words. Neshek, from a root meaning "to bite," and tarbit or marbit, meaning "increase." Exodus 22:25 says that if you lend money to the poor among God's people, you shall not be to him as a creditor and shall not exact neshek. Leviticus 25:35-37 extends it: if your brother becomes poor, take no interest or increase from him, and do not lend him food at a profit. Deuteronomy 23:19-20 is the one that caused all the trouble, because it forbids charging your brother and then explicitly permits charging a foreigner (nokri).

Then there are the moral texts. Psalm 15:5 describes the man who dwells on God's holy hill as one who does not put out his money at interest. Ezekiel 18 lists it three times (verses 8, 13 and 17) in its catalogue of the righteous man and the wicked one. Nehemiah 5:7-11 has Nehemiah furiously confronting the nobles for exacting interest from their own countrymen during a famine and making them return the fields and the hundredth part of the money.

The New Testament is thinner than people assume. Luke 6:34-35 tells disciples to lend expecting nothing in return, which sounds decisive until you notice the context is generosity toward enemies rather than a commercial rule. And in the parable of the talents (Matthew 25:27, with the parallel at Luke 19:23) the master rebukes the servant for not putting the money with the bankers to collect interest. That verse sat awkwardly in every medieval treatise on the subject.

Luther did not legalize anything

Luther's position hardened over his life rather than softening. His early sermons on usury (1519 and 1520) attacked the practice hard, and Trade and Usury in 1524 went after merchants and lenders together. By 1540, in his open letter to pastors urging them to preach against usury, he was calling usurers thieves and murderers and pressing for them to be excluded from the sacrament.

He did make one concession, and it is the one people misread. The Zinskauf, the rent-charge or census contract, involved buying an annual income stream secured on productive land. Luther grudgingly allowed that such a purchase could be legitimate at a modest rate (roughly four to six percent was the customary range) provided the buyer genuinely shared in the risk of the land failing. The moment the lender was guaranteed his return regardless of the harvest, Luther said the contract had become usury wearing a costume.

What Luther offered there was a narrow risk-sharing exception rather than a theory of interest, and the logic is close to what Islamic jurists say about the difference between a genuine musharaka partnership and a fixed obligation dressed up as one.

Calvin's letter, and what it actually argued

The document that changed the conversation was a private letter Calvin wrote around 1545 to Claude de Sachin, a friend who had asked whether lending at interest could ever be lawful. Calvin never published it. It circulated in manuscript and appeared in print after his death as De usuris responsum. The letter is short, and its reasoning runs roughly like this.

First, Calvin dismantled the Aristotelian argument that money is barren and therefore cannot justly produce a return. Aquinas had leaned on it in the Summa Theologiae (II-II, q. 78), where usury is selling what does not exist, because in a loan of a fungible good the use is inseparable from the thing itself. Calvin's counter was empirical: a man who buys a field with borrowed money makes the money fruitful, so calling coin sterile describes the metal rather than the transaction.

The Deuteronomy problem

Second, and more importantly, he refused to read Deuteronomy 23:20 as a permanent license to fleece foreigners. He treated the brother/stranger distinction as part of Israel's judicial and political law, bound to a particular polity, rather than a standing moral rule. Once you say that, the entire medieval scaffolding wobbles, because the prohibition texts have to be re-grounded in something other than a literal statute.

Calvin re-grounded them in equity. His controlling principle was the Golden Rule (Matthew 7:12) and the command to love the neighbor as oneself (Leviticus 19:18). The question stopped being "did money change hands at a premium" and became "did this transaction oppress the borrower."

The conditions he attached

This is the part that gets dropped from the popular summary. Calvin hedged his conclusion with a series of restrictions, and secondary literature usually enumerates them as a list of seven. The substance is consistent across the manuscript tradition: do not take interest from the poor; do not become so absorbed in lending that you neglect your duty to the needy; require nothing contrary to natural equity; let the borrower gain as much or more than the lender; judge by the Word of God rather than by what everybody else is doing; consider the common good of the commonwealth, not just the parties; and do not exceed the rate the civil authority permits.

He also said, plainly, that he wished the practice were banished from the world entirely and that he was giving a reluctant answer to a hard case rather than an endorsement. Geneva's council backed this up with a hard statutory cap in the low single digits, adjusted upward later for merchant lending. A Genevan lender operating under Calvin's actual regime had less freedom than a modern credit card issuer has by several orders of magnitude.

How "usury" quietly became "excessive interest"

The semantic shift did not happen in one letter. Three things moved at once.

The canonists had already been carving out exceptions for two centuries. Damnum emergens (loss the lender actually suffers) and lucrum cessans (profit foregone) let a lender recover something without the payment counting as usury on the loan itself. The contractus trinus, or triple contract, combined a partnership, an insurance of the principal and a sale of the uncertain profit for a fixed one, producing a guaranteed five percent that Johann Eck defended publicly at Bologna in 1515 with Fugger money behind him. And the Fifth Lateran Council in that same year approved the montes pietatis, the charitable pawn banks, allowing them to charge a modest fee for expenses while restating that usury means gain sought from a loan involving no labor, cost or risk.

Meanwhile the civil law moved. England's 1545 statute under Henry VIII permitted lending up to ten percent, was repealed under Edward VI in 1552, and came back under Elizabeth in 1571 with a rate ceiling attached and language still calling the practice sinful. Once a legal maximum exists, the word "usury" has somewhere new to go: it attaches to the rate above the line.

And the jurists finished the job. Charles du Moulin's 1546 treatise on contracts and usury argued from within the Catholic legal tradition that moderate interest on commercial loans was defensible, and the Salamanca school (Domingo de Soto, Martín de Azpilcueta) was working through exchange, time and money value on similar lines. Calvin gave the argument theological cover in Protestant territory, but he was joining a movement rather than starting one.

The strongest case against the standard story

There is a serious minority position that says the Reformation changed nothing that matters, and it deserves a fair hearing.

The argument runs that Calvin's letter is being asked to carry weight it was never built for. It was a private pastoral response to one man's question, it explicitly refused to give a general rule, and it attached conditions that essentially no modern consumer lender satisfies. Reading it as a charter for the interest economy inverts its plain intent. Critics also press the exegetical point: if you can dissolve Deuteronomy 23:20 into "judicial law for Israel," you have handed yourself a tool that can dissolve a great deal else, and the burden of proof for that move is higher than Calvin discharged in a few paragraphs.

The honest answer is that both sides are reading the same document correctly and disagreeing about what follows. Calvin did break the formal ban on all interest. He did not authorize interest as a neutral commercial fact, and later generations who cited him as if he had were quoting the conclusion while skipping the seven conditions.

Where this leaves a BRI screen

Biblically Responsible Investing inherited the post-Reformation settlement, and you can see it in the screens. The standard BRI categories are conduct and product exclusions: abortion, pornography, alcohol, tobacco, gambling and anti-family entertainment. Interest income is not on that list. Neither the BRI framework nor the USCCB socially responsible investment guidelines exclude banks or apply a leverage ratio, which is why a BRI-screened fund can hold JPMorgan (JPM) or Visa (V) without contradiction.

Compare that with the other frameworks a serious investor runs alongside it. AAOIFI-based Islamic screening applies a hard 30 percent ceiling on interest-bearing debt relative to market capitalization, a parallel 30 percent test on interest-bearing deposits and receivables, and a 5 percent cap on impermissible income including interest received. Under those rules the same bank is uninvestable outright. Halakhic screening under the ribbis prohibition permits interest from a non-Jewish counterparty and restructures Jewish-to-Jewish lending through a heter iska partnership document, which is functionally close to the risk-sharing logic Luther applied to the Zinskauf. LDS guidance says little about interest specifically and much more about debt and speculation, following the caution Dallin H. Oaks laid out in 1971.

If you run more than one lens, you will see the same holding come back clean under one and excluded under another. That is a real doctrinal disagreement showing up in your holdings, and the framework comparison is worth reading before you assume a screen covers something it does not.

What to actually do about it

Three practical moves.

Decide, explicitly, whether you are running a BRI screen or a hybrid. If you want interest exposure limited, you have to add that layer yourself, because standard BRI will not do it for you. FaithScreener surfaces interest income and interest-bearing debt as separate line items on every company report precisely so you can apply an Islamic-style ratio inside a Christian screen if that is your conviction. The screening methodology documents how each ratio is calculated and which financial statement line feeds it.

Look at where the interest comes from, not just how much. Calvin's conditions were about the character of the counterparty relationship. A regional bank earning net interest margin on small business loans and a subprime consumer lender charging thirty percent APR are treated identically by a percentage test and very differently by the equity principle Calvin was actually applying.

Watch leverage on non-financial holdings. A manufacturer carrying debt at four times market cap is paying interest as a structural feature of its operations, which is the exact situation Luther's risk-sharing test was designed to catch. You can screen a specific ticker and see the debt ratio before you decide whether it clears your own line.

The Bottom Line

The Reformation did not legalize interest. Calvin narrowed the prohibition from a blanket ban to a conduct test governed by equity, attached about seven restrictions to it, said he wished the practice would disappear, and lived under a civil rate cap in the low single digits. Luther went the other direction and got angrier about it with age. The modern definition of usury as merely excessive interest is a product of statutory rate ceilings, canon law exceptions and sixteenth-century commercial jurists working in parallel, and it took another two centuries to harden. The thing to remember: BRI screens do not test for interest at all, so if that gap bothers you on scriptural grounds, you have to close it deliberately rather than assume your Christian screen already did.

This is educational research rather than a religious ruling or personalized investment advice, so confirm the application to your own portfolio with a qualified pastor, scholar or financial advisor.