SOFR Index calculator

This calculator divides one published SOFR Index value by another and annualizes the result on an actual/360 basis, which gives the compounded average SOFR for any period the index covers. It is built for treasury, loan-operations and note-paying-agent staff who need to check a SOFR-in-arrears accrual against the New York Fed's own numbers rather than a spreadsheet of daily prints.

Features

• Published inputs only. The rate comes from two SOFR Index values exactly as the New York Fed published them, to eight decimals, so each end traces to an official number.
• Date snapping with an explanation. A weekend, holiday or out-of-range date moves to the nearest published index date, with a message saying which date was used.
• Interest two ways. Interest on the average rounded to five decimals and on the unrounded index ratio, so you see what rounding is worth.
• Independent cross-check. The same period is recompounded from the daily SOFR prints, and the difference from the index result is displayed.
• Comparison with published averages. When your period is exactly 30, 90 or 180 days, the NY Fed's published average for the end date is shown next to your result.
• CSV export. Every SOFR print in the period with its day weight and running compounding factor, followed by the two index values.

How to use the SOFR Index calculator

1. Enter the first day of the interest period as the start date. For a note with an observation shift, enter the shifted start of the observation period instead.
2. Enter the end date: the period end date (or shifted end), not the last day of accrual. The index on that date already includes the previous business day's SOFR.
3. Type a notional if you want the interest amount. Commas are accepted; leave it blank for the rate alone.
4. Read the compounded average, then check any date-snapping message and the daily-compounding cross-check.
5. Use Download CSV to keep the daily detail with your accrual file.

How the SOFR Index calculation works

What the SOFR Index is

The SOFR Index is a running product of daily SOFR compounding. The New York Fed set it to 1.00000000 on April 2, 2018, the first value date of SOFR, and compounds forward from there. It began publishing the index, together with the 30-, 90- and 180-day SOFR Averages, on March 2, 2020; the first official value, 1.04085026, already reflected compounding back to the April 2018 base. The latest value in this site's snapshot is 1.26208139 for October 9, 2026.

The index is published each business day shortly after SOFR itself, which the New York Fed releases at approximately 8:00 a.m. ET. Any revision happens the same day, at about 2:30 p.m. ET. Current and historical values are on the SOFR Averages and Index data page and on the New York Fed's SOFR Averages and Index page.

The formula and the conventions behind it

The New York Fed gives this formula for a compounded average between any two dates x and y:

Three conventions are baked into the index, and therefore into this result. SOFR compounds daily on business days. On weekends and holidays, the preceding business day's SOFR accrues as simple interest, so a Friday print normally counts for three days. The year is 360 days, with actual calendar days counted. Because those rules are already inside the published numbers, two divisions replace a loop over every print.

The result is rounded to five decimal places, the precision the New York Fed uses for its published averages. The index itself is rounded to eight decimals, so an average computed from it can differ from a published average in the fifth decimal place, as the New York Fed notes in its methodology documentation.

Worked example: the third-quarter 2026 interest period

The SOFR prints behind this result run from the July 1 value date through September 30. There are 64 of them, ranging from 3.53% (July 9) to 3.90% (September 25, 28 and 30). No SOFR was published for Friday, July 3, so the Thursday, July 2 print counted for four days; the September 4 print also counted for four days over the Labor Day weekend. The highest prints came after the federal funds target range moved from 3.50%–3.75% to 3.75%–4.00%, first shown in EFFR data for September 17, 2026, the day SOFR rose 23 bp. The CSV export lists every one.

Does the index match daily compounding?

It should, because the index is the same arithmetic done once by the administrator, and in our tests it does. For the example above, compounding the 64 daily prints with the compounded SOFR calculator's engine gives 3.6846971%, a difference of 0.0000002 percentage point from the index result. Across the full span of published index values in our data, March 2, 2020 to October 9, 2026 (2,412 days and 1,651 SOFR prints), the two methods agree to within 0.0000001 percentage point.

We also recomputed every published 30-, 90- and 180-day average whose window started on a published index date: 3,069 cases in the snapshot. The unrounded index result never differed from the published average by more than 0.000016 percentage point. After rounding to five decimals, 2,523 matched exactly, 545 differed by 0.00001 and one by 0.00002. The October 9, 2026 30-day average is one of the near misses: the index ratio from September 9 gives 3.8156970%, which rounds to 3.81570%, while the published figure is 3.81569%. That is the eight-decimal rounding of the index showing through, not an error in either number.

When to use the index, and when not to

Why notes and loans reference the index

The New York Fed publishes the index, in the ARRC's words, "to allow users to calculate a compound SOFR based on ISDA's definitions over any start and ending date." Two counterparties who look up the same two index values cannot disagree about holiday handling, day weights or floating-point drift across 60 or more daily factors. The ARRC's 2019 SOFR FRN Conventions Matrix made the same point: a published compounded SOFR index would avoid discrepancies in compounding formulas.

The index fits structures that weight each rate by the days of the observation period. One FRN convention the ARRC described is a two-day backward-shifted observation period with no lockout. Under it, the compounded rate equals the index ratio between the two shifted dates, so you enter those shifted dates here. That equivalence is our own derivation from the published definitions, and the NY Fed's formula covers it because it accepts any x and y.

Where the index does not fit

A lookback without an observation shift, which the ARRC's conventions contemplate for business loans with a five-business-day lookback, applies each rate for the days of the interest period rather than the observation period. The weights no longer line up with the index, so use the compounded SOFR calculator with its lookback or lockout setting. The same applies to periods that start before March 2, 2020, which this calculator cannot reach because no official index existed earlier; the compounding calculator works from daily SOFR back to April 2, 2018.

If your document references a published average set in advance rather than compounding in arrears, read the rate straight from the table below or the data page; the ARRC's user guide notes the averages "are more likely to be used in advance". The averages vs index guide covers that choice in detail.

Recent published SOFR Averages and Index values

The last ten publications from the New York Fed. Each average is a percentage to five decimals; the index is to eight.

Frequently asked questions

Why does the end date's index include only SOFR through the day before?

Index values carry a value date one business day after the last SOFR value date they include. The index for October 1, 2026 therefore contains SOFR through September 30, which is exactly what an interest period ending October 1 needs.

My period is 90 days but the result differs from the published 90-day average. Why?

Check the window first. The published average uses SOFR starting exactly 90 calendar days before its publication date, even if that day is a weekend or holiday, in which case the preceding business day's SOFR fills the gap. If your start date was moved to a published index date, your window is different. Where the windows agree, any remaining gap is at most a unit or two in the fifth decimal, from index rounding.

How does the calculator choose a date when mine has no index value?

It moves to the nearest published index date and, in a tie, to the earlier one. A Saturday therefore becomes the Friday before; a Sunday becomes the Monday after unless Monday is a holiday. Dates before March 2, 2020 or after the latest publication move to the first or last available value. The message under the buttons shows each change.

Should interest use the rounded rate or the index ratio?

Follow the calculation and rounding clause in your contract. The calculator shows both so you can see the size of the difference; in the worked example it is 8 cents on $10 million over 92 days.

Can I add a margin or spread?

Add it to the rounded average if your document applies the spread after compounding, then use the SOFR interest calculator for the dollar amount. For legacy LIBOR contracts that switched to SOFR, the LIBOR fallback calculator adds the fixed ISDA spread adjustment.

Is the SOFR Index the same as Term SOFR?

No. The index is backward-looking: it compounds overnight SOFR that has already been published. CME Term SOFR is a forward-looking rate built from SOFR futures, and using it requires a CME Group license, so this site does not display its values.

Privacy and data

All calculations run in your browser. The SOFR Index and daily SOFR values come from a dated snapshot of Federal Reserve Bank of New York data served from this site, and nothing you type, including the notional, is sent anywhere. Our sources and update process are described on the methodology page.