IBOR stands for Interbank Offered Rate, a family of benchmark interest rates that once measured what large banks said it would cost them to borrow unsecured funds from one another. The best-known member was LIBOR, the London Interbank Offered Rate, which at its peak anchored the pricing of roughly $400 trillion in loans, mortgages, and derivatives worldwide. Regulators retired LIBOR after banks were caught manipulating it and the underlying lending market withered, replacing it with transaction-based benchmarks such as SOFR.
What an Interbank Offered Rate Measured
An IBOR represented the rate at which major banks would lend unsecured funds to one another for a set period. The word “unsecured” carried the whole design: no collateral backed these loans, so the rate absorbed the risk that the borrowing bank might not pay it back. When confidence in banks fell, IBORs rose. When confidence returned, they fell.
IBORs were also forward-looking. A three-month LIBOR quote was a projection of borrowing costs over the next 90 days, not a record of what happened yesterday. That combination of forward-looking pricing and built-in bank credit risk made IBORs useful for pricing interest rate swaps, term loans, and other products where both sides needed a shared view of future funding costs.
The LIBOR Family
LIBOR was published in five currencies: the U.S. dollar, British pound, euro, Japanese yen, and Swiss franc. Each currency had multiple tenors, from overnight out to twelve months. Three-month U.S. dollar LIBOR was, for decades, the most referenced number in global finance.
Its reach went well past trading desks. Adjustable-rate mortgages, private student loans, corporate credit facilities, auto loans, and credit card agreements all used LIBOR as their floating reference. A homeowner in Ohio and a multinational in London were, in effect, paying interest based on the same panel of bank estimates submitted each morning in London.
How the Rate Was Set
Every London business morning, a panel of major banks answered a single question: at what rate could you borrow unsecured funds from another bank? Each submission was an estimate, not a report of a completed trade. The administrator collected the answers, discarded the top and bottom quartiles, and averaged what remained. If 16 banks submitted, the highest four and lowest four dropped out, and LIBOR was the simple average of the middle eight.1Bank for International Settlements. LIBOR and “Benchmark Tipping”: Then and Now
The trimming was meant to stop any single bank from pulling the number in its favor. It worked as long as submissions reflected a real market. When actual unsecured interbank lending shrank and the estimates became guesswork, even the trimmed average could be steered by a small group of coordinated submitters.
Why IBORs Were Retired
The Market Behind LIBOR Dried Up
After the 2008 financial crisis, banks largely stopped lending to each other on unsecured terms. They shifted to collateralized borrowing or central bank facilities. The volume of real transactions that were supposed to anchor LIBOR submissions collapsed, and a market-derived rate became an exercise in expert judgment.
In a July 2017 speech, Andrew Bailey, then head of the UK Financial Conduct Authority, said the market LIBOR claimed to measure was “no longer sufficiently active” and that a rate sustained by judgment rather than trades had an “inherently greater vulnerability to manipulation.” He announced that the FCA would stop compelling banks to submit LIBOR quotes after the end of 2021, setting a countdown for the rate’s retirement.2Financial Conduct Authority. The Future of LIBOR
The Manipulation Scandal
The vulnerability Bailey named was not hypothetical. Investigators in the U.S., UK, and Europe found that traders at major banks had submitted false rates for years. Some inflated or deflated their quotes to benefit derivatives positions. Others submitted artificially low rates during the financial crisis to make their institutions look healthier than they were.
Regulators imposed billions of dollars in fines on banks including Barclays and UBS. Individual traders faced criminal charges in both U.S. and UK courts. Two former Rabobank traders received prison sentences of one and two years after a federal jury convicted them of conspiracy to commit wire fraud and bank fraud tied to LIBOR manipulation.3U.S. Department of Justice. Two Former Rabobank Traders Sentenced to Prison for Manipulating US Dollar and Japanese Yen LIBOR
Structural decline and outright fraud pointed the same direction. A benchmark built on voluntary, unverifiable estimates from banks that stood to profit from the number could not be reformed into something dependable. It had to be replaced.
What Replaced IBORs
The successor benchmarks are called Risk-Free Rates, or RFRs. They differ from IBORs on every axis that mattered. RFRs are backward-looking rather than forward-looking, nearly free of bank credit risk, and calculated from large pools of completed overnight transactions instead of survey answers. That transactional foundation makes them far harder to manipulate.
Each major currency got its own replacement:
- U.S. dollar — SOFR: the Secured Overnight Financing Rate, based on overnight Treasury repurchase transactions, with daily volumes regularly above $3 trillion.4Federal Reserve Bank of St. Louis. Secured Overnight Financing Volume (SOFRVOL)
- British pound — SONIA: the Sterling Overnight Index Average, administered by the Bank of England.
- Euro — €STR: the Euro Short-Term Rate, published by the European Central Bank.
- Japanese yen — TONA: the Tokyo Overnight Average Rate, tracking the uncollateralized overnight call rate in Japan.5Bank of Japan. Interest Rate Benchmark Reform
- Swiss franc — SARON: the Swiss Average Rate Overnight, drawn from the Swiss repo market.
Because these rates measure collateralized or very short-term lending, they strip out the bank credit premium that was baked into LIBOR. Any credit component in a loan can now be added on top as a separate, visible spread rather than hidden inside the benchmark itself.
What This Meant for Existing Contracts
Panel-based LIBOR ceased on June 30, 2023, but decades of contracts still referenced it. Many had no fallback language, or their fallbacks pointed to methods that no longer worked, like polling banks for quotes. Two mechanisms handled the cleanup.
In the United States, Congress passed the Adjustable Interest Rate (LIBOR) Act, codified at 12 U.S.C. Chapter 55. The law automatically replaces LIBOR with a Federal Reserve Board-selected SOFR-based rate, plus the appropriate tenor spread adjustment, in contracts that lack a workable fallback or a designated party to pick one. It also creates a broad safe harbor: using the Board-selected rate is treated as “substantial performance,” does not breach the contract, and is not even considered an amendment.6Office of the Law Revision Counsel. 12 USC Chapter 55 – Adjustable Interest Rate (LIBOR)
Because SOFR runs lower than LIBOR by roughly the amount of the missing bank credit premium, a flat swap would have changed the economics of every legacy deal. The Alternative Reference Rates Committee recommended a fixed Credit Spread Adjustment, calculated from the five-year historical median difference between LIBOR and SOFR at each tenor, locked in as a permanent add-on so borrowers and lenders ended up roughly where they started.7Alternative Reference Rates Committee. ARRC Announces Recommendation of a Spread Adjustment Methodology for Cash Products
The FCA also allowed a temporary “synthetic” LIBOR, calculated from the relevant RFR plus a fixed spread, so certain legacy contracts had a published number to reference during the wind-down. Synthetic LIBOR was never available for new deals. The one-, three-, and six-month synthetic U.S. dollar LIBOR settings ceased permanently after their final publication on September 30, 2024.8Financial Conduct Authority. Remaining Synthetic US Dollar LIBOR Settings – Less Than 1 Month to Go Any contract still tied to LIBOR after that date relies on the LIBOR Act’s automatic conversion or whatever fallback the contract itself contains.
What Consumers Saw
If you held an adjustable-rate mortgage, a variable-rate student loan, a home equity line of credit, or a credit card indexed to LIBOR, your lender was required to switch the underlying index. Most moved to a SOFR-based rate; some shifted to the prime rate or another established benchmark.
The Consumer Financial Protection Bureau updated Regulation Z with specific notice requirements. Lenders replacing a LIBOR index on a home equity line of credit had to mail a change-in-terms notice at least 15 days before the new rate took effect. For open-end credit like credit cards, the lead time was 45 days. Both notices had to disclose the replacement index and any adjusted margin used to calculate the new rate.9Federal Register. Facilitating the LIBOR Transition (Regulation Z)
The credit spread adjustment was designed to keep payments roughly equivalent through the switch itself. What differs is behavior going forward: because SOFR tracks overnight Treasury repo rates rather than unsecured bank lending, it tends to move differently during banking-sector stress than LIBOR did. The direction of any advantage depends on where rates go from here. What the reform settled is that the benchmark under your loan is now built from actual transactions rather than a survey of the banks that price it.