SOFR: What It Is, How It Works & Why It Replaced LIBOR
How SOFR Works
SOFR is calculated from actual overnight repurchase agreement (repo) transactions collateralized by U.S. Treasuries. Every business day, the Fed collects data from three repo market segments: tri-party repo, General Collateral Finance (GCF) repo, and bilateral Treasury repo cleared through FICC.
The rate is published as a volume-weighted median of all eligible transactions from the prior business day. This means SOFR reflects where the bulk of actual borrowing happened — not where banks think they could borrow, which was LIBOR‘s fundamental weakness.
SOFR vs. LIBOR
| Feature | SOFR | LIBOR |
|---|---|---|
| Data Source | Actual repo transactions (~$1T+ daily) | Bank panel estimates (~$500M daily) |
| Credit Risk | Nearly risk-free (Treasury-backed) | Included bank credit risk premium |
| Tenor | Overnight (term rates derived via CME) | 7 tenors from overnight to 6 months |
| Manipulation Risk | Very low — based on massive transaction volume | High — subjective submissions were rigged |
| Volatility | Can spike at quarter/year-end due to repo dynamics | Generally smoother day-to-day |
| Administrator | NY Fed | ICE Benchmark Administration |
Key SOFR Variants
| Variant | Description | Use Case |
|---|---|---|
| Daily SOFR | The overnight rate published each business day | Overnight lending, daily compounding calculations |
| SOFR Averages | Compounded averages over 30, 90, and 180 days | Floating-rate notes, adjustable-rate mortgages |
| SOFR Index | Cumulative compounded value since April 2, 2018 | Calculating interest accrued over custom periods |
| CME Term SOFR | Forward-looking term rates (1, 3, 6, 12 months) | Business loans, swaps, legacy LIBOR contract replacements |
How SOFR Affects Financial Products
SOFR now serves as the reference rate across most USD-denominated financial products. Adjustable-rate mortgages reference SOFR instead of LIBOR. Corporate credit facilities are priced at SOFR plus a credit spread. Floating-rate bonds reset based on SOFR averages or term rates.
One key difference from LIBOR: because SOFR is a risk-free rate, lenders add a Credit Spread Adjustment (CSA) on top to compensate for the bank credit risk that was embedded in LIBOR. This ensures economic equivalence for contracts that transitioned from LIBOR to SOFR.
Limitations of SOFR
SOFR isn’t perfect. It’s an overnight rate, so it doesn’t naturally produce forward-looking term rates the way LIBOR did. The CME Term SOFR addresses this but depends on futures market liquidity. SOFR can also experience quarter-end and year-end volatility spikes when repo markets tighten — something that didn’t typically affect LIBOR.
Additionally, because SOFR is risk-free, it doesn’t reflect bank funding stress during crises. Some market participants argue this is a feature, not a bug — but it means SOFR plus a fixed spread may not fully capture real borrowing costs during periods of financial stress.
Key Takeaways
- SOFR is the primary USD benchmark rate, based on ~$1 trillion in daily overnight Treasury repo transactions.
- It replaced LIBOR because it’s grounded in actual transactions rather than subjective bank estimates.
- SOFR is nearly risk-free, so lenders add a credit spread to match the bank credit risk that LIBOR included.
- CME Term SOFR provides forward-looking rates (1, 3, 6, 12 months) similar to how LIBOR tenors worked.
- Watch for quarter-end and year-end repo market dynamics that can cause temporary SOFR spikes.
Frequently Asked Questions
What does SOFR stand for?
SOFR stands for Secured Overnight Financing Rate. It measures the cost of borrowing cash overnight using U.S. Treasury securities as collateral in the repo market.
Why did SOFR replace LIBOR?
SOFR replaced LIBOR because it’s based on actual transactions (roughly $1 trillion daily) rather than bank estimates that were susceptible to manipulation. The LIBOR scandal of 2012 accelerated the push for a more reliable benchmark.
How does SOFR affect my mortgage?
If you have an adjustable-rate mortgage originated after 2021, your rate likely resets based on SOFR plus a fixed margin. Older LIBOR-based ARMs have transitioned to SOFR with a credit spread adjustment to maintain economic equivalence.
Is SOFR a risk-free rate?
Nearly. SOFR is based on transactions collateralized by U.S. Treasury securities, which are considered risk-free. However, it still reflects repo market dynamics and can experience short-term volatility during periods of market stress.
What is Term SOFR?
Term SOFR is a forward-looking rate derived from SOFR futures prices, published by CME Group in 1-month, 3-month, 6-month, and 12-month tenors. It’s widely used in business loans and swaps because it provides rate certainty at the start of an interest period.