Sumerian Clay Tablets - Interest Records from 3000 BCE
The concept of interest emerged at roughly the same time as the invention of writing. The oldest surviving interest records are inscribed on clay tablets from the Sumerian civilization, dating to around 3000 BCE. In ancient Mesopotamia (present-day southern Iraq), a system was established for lending barley or silver and receiving repayment with interest after the harvest or a set period. The Sumerian word for interest, "mash," originally meant "calf" or "lamb." Just as livestock that are lent out produce offspring, grain or silver that is lent also "gives birth" to new value.
The Code of Hammurabi from Babylonia, dating to around 1800 BCE, contains detailed regulations on interest. The maximum interest rate for silver loans was set at 20% per year, and for barley loans at 33.3% (one-third) per year. Loans exceeding the maximum rate were declared void, and the creditor would forfeit the principal - a severe penalty. This is the world's oldest "interest rate cap law." People 5,000 years ago already recognized the dangers of high interest rates.
Compound Interest Problems Inscribed on Clay Tablets
Remarkably, ancient Babylonian mathematical texts (clay tablets) contain compound interest practice problems. A tablet from around 1700 BCE records the problem: "If 1 mana of silver is lent at 20% annual interest, how many years until the total principal and interest doubles to 2 mana?" This is the same question as the modern "Rule of 72." At 20% annual interest, 72 / 20 = 3.6 years, but the Babylonians used their base-60 number system to calculate precisely, arriving at an answer of approximately 3 years, 9 months, and 5 days.
The Babylonian mathematicians' ability to perform compound interest calculations was underpinned by their sophisticated mathematical system. Base-60 notation (which survives today in our units of time and angles), positional numeration, reciprocal tables, and square root approximations - Babylonian mathematics was remarkably advanced. The concept of exponentiation needed for compound interest was also organized in numerical tables on clay tablets. Compound interest is not a "modern invention" but a mathematical concept humanity has worked with since the dawn of civilization.
Religion and Interest - 3,000 Years of Prohibition and Acceptance
The history of interest is also a history of religious prohibition. Deuteronomy 23:19-20 in the Old Testament commands, "You shall not charge interest to your brother." However, the exception "you may charge interest to a foreigner" was one factor that led to Jewish involvement in finance in medieval Europe. Christianity also prohibited interest (usury) throughout the Middle Ages, and the Second Lateran Council of 1139 declared that those who charged interest would be excommunicated.
The Quran (2:275-276) also explicitly prohibits interest (riba). This prohibition carries over into modern Islamic finance, which conducts financial transactions through mechanisms such as profit-sharing (mudarabah), cost-plus financing (murabaha), and leasing (ijara) instead of interest. Total Islamic finance assets reached approximately $4 trillion as of 2024, demonstrating that a financial system without interest can function at massive scale.Books on financial history contain even more detailed accounts of the tension between religion and economics over interest.
The Role Interest Has Played in Civilizational Development
Despite repeated attempts to ban it, interest never disappeared. The reason is that interest serves functions essential to economic activity. First, interest is "the price of time." One million yen today and one million yen a year from now do not have the same value. Interest puts a price on this time difference, making it possible to exchange present consumption for future consumption.
Second, interest is compensation for risk. It provides lenders who bear the risk of non-repayment with a reward commensurate with that risk. Without interest, no one would have an incentive to lend money to others, making business investment and home purchases extremely difficult. Third, interest promotes efficient allocation of resources. A business willing to pay high interest is one that expects correspondingly high returns. Through the signal of interest rates, capital flows toward its most productive uses. The interest system invented by the Sumerians 5,000 years ago continues to underpin the modern financial system, albeit in evolved forms.
Next Actions - Lessons from 5,000 Years of History
The greatest lesson from the history of interest is that "interest can be either ally or enemy." As a depositor or investor receiving interest, compound interest grows your assets like a snowball. As a borrower paying interest, compound interest accelerates debt at an increasing rate. The Code of Hammurabi established maximum interest rates 3,800 years ago to control the "enemy" side of interest. What we can do today is build a household financial structure that minimizes the interest we pay (debt) and maximizes the interest we receive (investments). Start by listing all the interest you currently pay (mortgage, card loans, revolving credit) alongside all the interest you receive (deposits, investments).