EONIA

EONIA, the Euro Overnight Index Average, was a benchmark for the effective rate in the unsecured overnight euro interbank lending market. It is no longer published: EONIA was discontinued on January 3, 2022, after a transition in which its calculation was changed to the euro short-term rate (€STR) plus a fixed spread of 8.5 basis points.

EONIA now matters mainly for historical data, legacy contract interpretation, and understanding the development of euro overnight-index markets. €STR is the current euro overnight benchmark.

Key Takeaways

• EONIA is discontinued and should not be presented as a current euro benchmark.
• Before October 2019, EONIA was transaction-based and measured unsecured overnight interbank lending.
• From October 2, 2019 until cessation, EONIA equaled €STR plus 8.5 basis points.
• EONIA and €STR measured opposite sides of funding activity: lending versus borrowing, with different market coverage.
• Historical EONIA contracts and curves require transition, fallback, and date-specific methodology review.

What EONIA Originally Measured

Under its earlier methodology, EONIA represented the volume-weighted average rate on eligible unsecured overnight euro lending transactions reported by a panel of banks. It described the lending side of the euro interbank overnight market.

A simplified volume-weighted average is:

where (r_i) is an eligible transaction rate and (V_i) is its volume. The official methodology controlled participant eligibility, reporting, filtering, and publication.

EONIA was used extensively in overnight index swaps, collateral remuneration, cash products, valuation, and euro interest-rate curve construction. That broad use made a reliable transition essential when the old methodology could no longer satisfy the desired benchmark standards.

Why EONIA Was Replaced

The working group on euro risk-free rates identified weaknesses in the earlier EONIA market base, including limited underlying transactions and concentration among contributors. Those conditions raised concerns about robustness and compliance with the European benchmark framework.

The European Central Bank developed €STR as a broader transaction-based measure of unsecured overnight euro wholesale borrowing costs. The working group recommended €STR as EONIA’s replacement.

Rather than stop EONIA immediately, authorities and market participants used a transition period so contracts, systems, and valuation processes could migrate.

The €STR Plus 8.5 Basis Point Method

From October 2, 2019, EONIA was no longer calculated directly from its old panel transaction set. It became:

Because one basis point is 0.01%, 8.5 basis points equals 0.085 percentage point.

The fixed spread was derived from historical differences between pre-€STR data and EONIA over a defined observation period. It provided a stable bridge; it was not a prediction that the economic difference would always remain 8.5 basis points.

Worked Example: Transitional EONIA

Suppose €STR for a historical transition-period date was -0.550%. The corresponding EONIA calculation was:

For a notional EUR 20 million overnight balance accruing for one day on an Actual/360 basis, illustrative interest would be:

The negative amount illustrates the negative-rate environment and does not determine which party pays under a specific contract. The agreement’s sign convention, floor, and payment terms control.

EONIA Versus €STR

The fixed transition relationship means the two series moved mechanically together after October 2019. It does not mean pre-transition EONIA can be converted into a perfect synthetic €STR history by subtracting 8.5 basis points without documenting methodology differences.

EONIA Versus EURIBOR

EURIBOR is an active euro term benchmark published for one week through twelve months. EONIA was an overnight benchmark.

The fact that both names begin with “Euro” does not make them alternative tenors of one benchmark.

How EONIA Appears in Historical Analysis

Analysts may encounter EONIA in:

• pre-2022 overnight index swaps and curve data
• collateral and cash-remuneration agreements
• fund prospectuses and performance benchmarks
• central-bank and money-market research
• valuation models with archived discount curves
• accounting records for transitioned derivatives

For each use, determine whether the data date falls before or after the October 2019 methodology change. A chart spanning that date contains a structural break even if the ticker is unchanged.

Reviewing a Legacy EONIA Reference

Confirm:

1. the transaction and valuation dates
2. whether the old transaction methodology or €STR-plus-spread methodology applied
3. the compounding, averaging, and day-count convention
4. the cessation or benchmark-replacement trigger
5. whether the document was amended to reference €STR directly
6. any spread, payment delay, observation shift, or rounding change
7. whether a related hedge transitioned on matching terms

An old document can still display “EONIA” even when a later amendment determines the operative rate.

Common Mistakes

• Describing EONIA as the current ECB euro overnight rate.
• Saying EONIA was always calculated as €STR plus 8.5 basis points.
• Applying the transition spread to pre-October 2019 observations without qualification.
• Treating EONIA and EURIBOR as overnight and term settings of one family.
• Ignoring the methodology break in a historical time series.
• Adding 8.5 basis points to €STR after a contract has already transitioned to direct €STR.
• Assuming a negative benchmark automatically determines the direction of a contractual payment.

Sources and Further Reading

• European Central Bank glossary, EONIA and €STR
• ECB working group, transition from EONIA to €STR
• ECB, EONIA data-series methodology
• ECB, Euro money market study 2022

Related Terms

• €STR: The active benchmark that replaced EONIA.
• EURIBOR: The active euro unsecured term benchmark.
• Alternative Reference Rates: The broader transition category that includes €STR.
• Overnight Rate: The one-day funding-rate concept underlying EONIA and €STR.
• Overnight Index Swap: A major historical use of EONIA.

FAQs

This article provides general financial education, not personalized investment, borrowing, accounting, tax, or legal advice. Use current official sources and governing documents for valuation or settlement.