If you grew up hearing that Jews can't charge or pay interest, and then you noticed Israeli banks exist and your frum uncle has a mortgage, you probably wondered what's going on. The answer is a 500-year-old legal document called the heter iska, and it's one of the most creative pieces of rabbinic financial engineering ever written.

Let me walk you through what it actually is, why it exists, and how it matters for anyone trying to build a halakhic investment portfolio in 2026.

The Problem: Ribbit in Plain Torah Text

The Torah is blunt about interest. Leviticus 25:36 says, "Take no interest from him, neither increase, but fear your God, that your brother may live with you." Then in 25:37, "You shall not lend him your money upon interest, nor give him your food for increase." Deuteronomy 23:20 adds, "You shall not lend upon interest to your brother."

The Talmud expands this in tractate Bava Metzia, especially chapter 5 (Eizehu Neshech), which spends roughly 30 folio pages defining what counts as forbidden interest. The rabbis created categories: ribbit d'oraita (biblically forbidden interest) and ribbit d'rabbanan (rabbinically forbidden interest, which catches even creative workarounds). They also forbade avak ribbit, the "dust of interest," which covers indirect benefits that feel like interest even if they aren't technically structured that way.

By the time you finish reading Yoreh Deah 160-177 in the Shulchan Arukh, the prohibition is airtight. No direct loans at interest. No backdoor benefits. No preferential treatment in exchange for the loan. Nothing.

Which creates an obvious problem once you want to run a bank.

Enter Rabbi Menahem Mendel of Krakow

The heter iska ("permission for a business partnership") is typically traced to Rabbi Menahem Mendel Avigdors of Krakow around 1600, though earlier versions existed. The insight was simple: the Torah forbids lending at interest, but it doesn't forbid partnerships where one party provides capital and the other provides labor, with profits shared.

That's a silent partnership. It's kosher. So why not structure every "loan" as a partnership?

The heter iska document does exactly that. Instead of Bank A lending $100,000 to Borrower B at 5% interest, the document says Bank A is investing $100,000 in Borrower B's business as a silent partner. Borrower B agrees to manage the capital and share profits. The "interest" is redefined as the bank's share of expected profits from the venture.

There's more structure behind it. The document typically splits the capital into two parts: half is a pikadon (deposit, held at Borrower B's risk) and half is a milveh (loan, held at Borrower A's risk). This mixed structure ensures the transaction can't collapse into either pure lending or pure investment in a way that would violate halakha.

The document also requires the borrower to swear an oath or accept a penalty if they claim the business lost money, unless they can produce witnesses. Which means in practice, borrowers almost always pay the agreed amount rather than try to prove losses. The practical outcome looks identical to a conventional interest-bearing loan, but the legal structure is genuinely a partnership.

Does It Actually Work?

Rabbinic opinion is split on how seriously to take the heter iska. The mainstream Orthodox view, codified in the Shulchan Arukh Yoreh Deah 167, accepts heter iska as a legitimate way to conduct business between Jews. Bank Leumi, Bank Hapoalim, and every other Israeli bank has a heter iska on file with the Chief Rabbinate of Israel. So do most Orthodox credit unions and gemachs (free loan funds) when they need to structure transactions with any financial component.

The Chazon Ish (Rabbi Avraham Yeshaya Karelitz) was more cautious, warning that heter iska should be used only when necessary and not as a casual workaround. Rabbi Moshe Feinstein (Igrot Moshe, Yoreh Deah 2:62) permitted heter iska broadly for commercial transactions but was more restrictive for personal loans between individuals.

The Satmar Rebbe and some Hasidic communities are stricter, arguing that heter iska has become a fig leaf that effectively nullifies the ribbit prohibition. These communities sometimes maintain their own free loan societies rather than use bank credit.

For practical purposes in 2026, if you're banking in Israel or using an Orthodox-affiliated institution in the US, you're almost certainly transacting under a heter iska whether you asked for one or not.

How This Applies to Stock Investing

Here's where it gets interesting for portfolio construction. Heter iska was designed for loans, not stocks. But the underlying logic extends to any situation where Jewish investors want to participate in an interest-bearing financial structure.

The most obvious application: buying shares in a bank. A halakhic investor who wants to own JPMorgan Chase (JPM), Bank of America (BAC), or Wells Fargo (WFC) faces a question. These companies earn most of their revenue from lending at interest. If Jewish shareholders are partial owners of the bank, are they participating in forbidden ribbit?

Rav Moshe Feinstein's position, which is widely followed, is that owning stock in a publicly traded bank is permitted because shareholders don't actually issue loans or collect interest directly. They own a pro-rata share of the corporate entity, which is a separate legal person. The corporation makes the loans. The shareholder receives dividends derived from corporate earnings. The direct lender-borrower relationship doesn't exist between the shareholder and the bank's customers.

This is essentially the same logical move the heter iska makes: insert a legal structure between the Jew and the interest transaction that transforms the relationship.

Other authorities, like Rabbi Yitzchok Breitowitz, have argued that Jewish investors in conventional banks should ideally hold a personal heter iska to cover their participation. This is a minority view but shows how seriously some treat the question.

Real Portfolio Implications

If you're building a halakhic screened portfolio and you want bank exposure, your options are:

Option 1: Hold bank stocks under the majority Feinstein position. You can own JPM, BAC, WFC, Citigroup (C), Goldman Sachs (GS), and similar names. The reasoning is that corporate form insulates shareholders from direct ribbit exposure. This is what most Orthodox Union kosher certification programs accept for retirement accounts.

Option 2: Use a heter iska investment fund. Some Israeli investment houses, like Excellence Investments and IBI (Israel Brokerage and Investments), offer funds that explicitly operate under heter iska for fixed-income exposure. These are more common in Israel than the US.

Option 3: Avoid bank stocks entirely. The strictest position, held by some Haredi communities, is to exclude financial services from portfolios. This is closer to how AAOIFI Shariah screening handles banks, and it dramatically reduces your investable universe. You'd be cutting roughly 15% of the S&P 500 (XLF, the financial sector ETF, represents about 13-14% of the index most years).

Option 4: Buy the business but not the interest income. Some screeners (including ours at FaithScreener) tag companies by the percentage of revenue from interest income. Payment processors like Visa (V) and Mastercard (MA) earn most revenue from transaction fees, not interest. Even though they're classified as "financial," their income stream is halakhically cleaner than a traditional bank.

The Mishnah on Indirect Interest

The Mishnah in Bava Metzia 5:2 gives a classic example of forbidden interest: "If one lent another money, he may not dwell in his courtyard for free, nor rent it at a lower rate, because this is interest." The principle is that any benefit flowing from borrower to lender because of the loan is ribbit, even if it's not cash.

This matters for stock investing because it means you can't accept any benefit tied to a loan relationship. If you own shares in a company that holds your mortgage, and the company gives shareholders preferential mortgage rates, that preferential rate could be considered avak ribbit. In practice this rarely comes up, but it's the reason some strict authorities don't like the idea of Orthodox Jews holding shares in their own lender.

What Heter Iska Doesn't Fix

The heter iska handles the ribbit problem. It does not fix other halakhic issues with an investment. If you use a heter iska structure to invest in a pork-processing company or a wine importer, you've solved the interest question but you've created new problems (treif products, yayin nesech concerns).

Think of heter iska as one filter in a stack. For a fully halakhic portfolio you still need to screen for:

Business activity (no idolatry-adjacent businesses, no treif)
Chametz on Pesach (ownership of chametz-holding companies during Passover is debated)
Shabbat desecration (companies that operate on Shabbat are a separate question with more flexible rulings)
Mixed funds (does the company engage in forbidden lending to other Jews?)

Practical Screening Checklist

For an investor building a heter iska-compatible portfolio, here's a practical checklist based on how we've seen Orthodox investment advisors approach it:

Confirm your brokerage or investment advisor has a standing heter iska for any margin or interest-bearing account features. Many kosher-certified advisors do this automatically.
For bank stocks (JPM, BAC, WFC, C, GS), default to the Feinstein position unless your personal rabbi tells you otherwise.
For REITs, check if the underlying rentals involve interest-bearing financing structures. Most REITs are fine under the shareholder-separation logic.
For insurance companies (Berkshire Hathaway, BRK.B, or Progressive, PGR), most authorities permit them because the insurance business is contingent payment, not interest.
Avoid pure lending businesses structured as LLCs or partnerships (not corporations) where you become a direct partner in the lending activity. That's where the shareholder-separation argument weakens.

One Last Thing

The heter iska was invented because Jewish communities needed to function economically in a world that runs on credit. It was not meant to erase the ribbit prohibition, just to let observant Jews participate in commerce without constantly stepping on Torah prohibitions. The best way to think about it: if you're using a heter iska structure without thinking, you're probably missing the point. If you're using it deliberately because you've thought about the tradeoffs and consulted a competent rabbi, you're doing what the document was designed for.

For most modern investors in a publicly traded stock portfolio, the heter iska itself rarely needs to be invoked directly. What matters more is the downstream logic it enabled: that corporate structures, silent partnerships, and pro-rata ownership can let Jewish investors participate in a market economy without crossing clear halakhic lines. That principle, more than the document itself, is why a halakhic investor in 2026 can own a diversified index fund at all.

Heter Iska: The Rabbinic Workaround for Interest-Based Investing