SOFR interest calculator
Interest on a principal at SOFR plus a spread for any accrual period, priced off the latest SOFR (3.87% for October 8, 2026), a SOFR Average, compounded SOFR in arrears or a rate you enter.
This calculator answers the question a treasury desk or loan administrator asks every period: how many dollars of interest does this principal earn or cost between two dates at SOFR plus a spread? Pick the SOFR basis your contract uses, enter the spread in basis points and the day-count basis, and it returns the interest, the all-in rate and a split between the SOFR portion and the spread portion.
Calculate interest at SOFR + spread
The calculator runs in your browser and needs JavaScript. The worked example below walks through the same calculation by hand.
Features
- Four SOFR basesThe latest published SOFR, the latest 30-, 90- or 180-day SOFR Average, compounded SOFR in arrears over your exact dates, or a rate you type in.
- Compounding done the New York Fed wayBusiness-day compounding, with weekend and holiday days accruing at the prior business day's SOFR, on actual days over 360. Every fixing is listed in a table you can check.
- Spread kept separateThe result splits interest into the part earned by SOFR and the part earned by the margin, the split you need to reconcile a rate notice line by line.
- Four day-count basesACT/360, ACT/365 Fixed, 30/360 and ACT/ACT (ISDA), so you can match the interest clause in the agreement, not an assumed one.
- Compounded-margin comparisonIn compounded mode it also shows what the period would cost if the spread were compounded daily with SOFR, so you can see what that drafting difference is worth.
- CSV exportOne click downloads the inputs, the result and, for compounded SOFR, every daily fixing, ready for a spreadsheet tie-out.
How to use the SOFR interest calculator
- Enter the principal and the accrual dates. The start date accrues; the end date does not, so a period from July 1 to October 1 is 92 days of interest.
- Choose the SOFR basis your document specifies. Pick compounded SOFR for a loan or note that accrues in arrears, a SOFR Average for a rate set in advance from the averages, or type a rate if you already have the fixing.
- Enter the spread in basis points and choose the day-count basis from the interest clause. SOFR itself is compounded on actual days over 360, so ACT/360 is the default.
- Read the interest, the all-in rate and the breakdown. The formula line underneath prints the exact arithmetic so you can reproduce it.
- Use Download CSV to keep the inputs and, for compounded SOFR, the daily fixings alongside your own records.
How the interest is calculated
The formula
Whatever the SOFR basis, the calculator applies simple interest for the period at an all-in rate:
The year fraction comes from the day-count basis. Under ACT/360 it is the number of calendar days in the period divided by 360; under ACT/365 Fixed the same days divided by 365; under 30/360 every month counts as 30 days; and under ACT/ACT (ISDA) the days falling in each calendar year are divided by that year's length, 365 or 366. The day count calculator shows the four side by side for any pair of dates.
For compounded SOFR in arrears, the SOFR basis is the compounded rate the New York Fed uses for its own SOFR Averages:
Why the spread is added after compounding
When interest accrues on compounded SOFR in arrears plus a margin, the usual structure compounds only SOFR and adds the margin to the resulting rate:
Split that open and the base interest equals principal × (Π − 1) exactly, while the spread accrues as plain simple interest on the principal. That is how the ISDA fallback rate for USD LIBOR was built: compounded SOFR in arrears plus a fixed spread adjustment, with the spread added after compounding rather than compounded itself. The credit spread adjustment guide covers those fixed values.
The alternative, compounding SOFR + spread together each day, earns interest on the margin and costs the borrower slightly more. The calculator shows that figure (on ACT/360) next to the standard one; if your document compounds the margin, use it.
Conventions and assumptions
SOFR is quoted on an actual/360 basis, and the compounded rate is annualized on 360 days by construction. ACT/360 is therefore the default and the only basis on which principal × (Π − 1) equals the base interest. Some agreements use the other bases, but pairing compounded SOFR with ACT/365 Fixed cuts interest by about 1.4%, so check the contract really says so.
In compounded mode the calculator uses plain compounding in arrears: each day's SOFR accrues for that day, with no lookback, observation shift or lockout. If the period starts on a weekend or holiday, the preceding business day's SOFR covers those first days, which is the treatment the New York Fed applies to the start of its averages windows. Loans and notes that use a lookback or shift observe different SOFR dates; the compounded SOFR calculator handles those conventions, and compounding in arrears conventions explains why they exist.
The latest SOFR and SOFR Average options apply one rate to the whole period, as a rate set in advance would: useful for projecting the next period, but not the compounded result.
Worked example: one quarter of 2026
Take $10,000,000 at compounded SOFR in arrears + 150 bp, ACT/360, accruing from July 1, 2026 to October 1, 2026. These are the calculator's defaults.
Step 1: compound SOFR. The period is 92 calendar days and uses 64 SOFR fixings, for value dates July 1 to September 30, 2026. SOFR ran between 3.53% and 3.68% through mid-September; no SOFR was published for July 3, so the 3.64% for July 2 accrued for four days. On September 17, the day a 3.75%–4.00% federal funds target range took effect, SOFR moved from 3.62% to 3.85% and stayed between 3.85% and 3.90% to the end of the month. Multiplying the 64 daily factors gives Π = 1.00941645, so compounded SOFR is (1.00941645 − 1) × 360 / 92 = 3.68470%.
Step 2: cross-check with the SOFR Index. The New York Fed's SOFR Index was 1.24923010 on July 1 and 1.26099341 on October 1, 2026. (1.26099341 / 1.24923010 − 1) × 360 / 92 = 3.68470%, the same rate. The SOFR Index calculator does this for any pair of dates.
Step 3: add the spread and accrue. The all-in rate is 3.68470% + 1.50% = 5.18470%. Interest is $10,000,000 × 5.18470% × 92 / 360 = $132,497.82, made up of $94,164.48 of base interest and $38,333.33 of spread interest. The base interest equals $10,000,000 × (1.00941645 − 1), as it should.
The same principal, dates and spread priced other ways:
| Method | SOFR basis | Interest | vs. standard |
|---|---|---|---|
| Compounded SOFR in arrears + spread, ACT/360 (standard) | 3.68470% | $132,497.82 | — |
| SOFR and spread compounded together daily, ACT/360 | 3.68470% | $132,923.62 | +$425.80 |
| Compounded SOFR in arrears + spread, ACT/365 Fixed | 3.68470% | $130,682.78 | −$1,815.04 |
| SOFR for July 1, 2026 set in advance, ACT/360 | 3.66% | $131,866.67 | −$631.15 |
| 90-day Average SOFR published July 1, 2026, set in advance, ACT/360 | 3.63493% | $131,225.99 | −$1,271.83 |
The rates set in advance came in lower because they were fixed before the September 17 move; in a falling-rate quarter the ordering reverses. Arrears tracks what overnight funding actually cost, while in-advance tells you the payment on day one.
Who should use it, and the caveats
Who it is for
Corporate treasurers checking a lender's interest notice, loan administrators and agents reconciling accruals, investors in SOFR notes estimating the next coupon, and finance teams budgeting next quarter's interest cost all need this calculation. For an amortizing loan over several periods, use the floating-rate loan calculator; to turn a basis-point move into dollars, the basis point calculator; for legacy LIBOR contracts that fell back to SOFR plus a spread adjustment, the LIBOR fallback calculator.
What the calculator cannot tell you
Estimates, not contract amountsThis page produces estimates for checking and planning. The interest you owe or receive is set by your agreement and the calculation agent, and it can differ for reasons the calculator does not model: rounding of the compounded rate or the daily factors, a lookback, observation shift or lockout, a SOFR floor, a different business-day calendar, or the agent's own rounding of the final amount. Where they differ, the contract governs. Nothing here is investment, legal or tax advice.
Compounded SOFR in arrears is only known once the last fixing in the period is published, so this mode accepts end dates up to the business day after the latest SOFR in the snapshot (October 8, 2026). For a later period, use the latest SOFR or a SOFR Average as an estimate and expect the final figure to move with SOFR. The calculator never displays CME Term SOFR, which is a licensed benchmark; if your loan uses Term SOFR, type the rate from your rate notice into the manual option.
Frequently asked questions
- Why does SOFR interest use a 360-day year?
- SOFR is a money-market rate, and the New York Fed quotes and compounds it on actual days over 360. A 92-day period has a year fraction of 0.255556, not 0.252055 as on ACT/365 Fixed.
- Is compounded SOFR + spread the same as compounding SOFR + spread daily?
- No. Adding the spread after compounding means the margin earns simple interest only. Compounding the two together earns interest on the margin as well. On the July 1 to October 1, 2026 example the difference is $425.80 on $10 million at 150 bp, and it grows with the spread, the rate level and the length of the period.
- Why is my lender's figure different?
- An agreement may round the compounded rate, apply a floor, or use a lookback rather than plain arrears; the ARRC's conventions for business loans contemplate a five-business-day lookback. Rounding moves the result by cents or dollars, but a lookback can move it by hundreds: on the default example a five-business-day lookback gives $131,998.82, about $499 less, because it misses part of the September 17 rise. A floor above SOFR can move it far more. Compare the SOFR dates in the daily table with the observation dates in your notice first.
- Which SOFR Average should I pick?
- The one your document names. The tenor normally lines up with the rate it replaced or the length of the interest period: Regulation ZZ, for example, replaced one-month LIBOR in FFELP asset-backed securities with the 30-day Average SOFR and three-month LIBOR with the 90-day Average SOFR, each plus a fixed spread. The averages are compounded SOFR over the 30, 90 or 180 calendar days before their publication date; the SOFR Averages and Index page charts their history.
- Can I enter a negative spread?
- Yes. A negative spread lowers the all-in rate, for pricing set below SOFR. The calculator also accepts fractional basis points, such as the 26.161 bp three-month spread adjustment.
Privacy and data
All calculations run in your browser. The SOFR and SOFR Averages come from a dated snapshot of Federal Reserve Bank of New York data, through October 8, 2026, served from this site; the compounding and interest figures are BitsSecurity's own calculations, not New York Fed figures. Nothing you type is sent anywhere or stored.