Sterilized intervention

What is sterilized intervention

Sterilized intervention is a central bank operation in the foreign exchange market where the bank also cancels out the effect of that operation on the domestic money supply.

Forex intervention is when a central bank buys or sells foreign currency to influence its own currency's exchange rate. Sterilization is the follow-up step that keeps local liquidity where it was.

Formal definition

A central bank's monetary base is backed by net foreign assets (NFA) and net domestic assets (NDA). An FX intervention changes NFA. Sterilization is an offsetting change in NDA of the same size, so the monetary base stays roughly unchanged. Only the composition of the balance sheet changes.

If the offset is smaller than the intervention, it is called partial sterilization. If there is no offset, the intervention is unsterilized and works like a change in monetary policy.

Worked example (hypothetical)

Suppose the rupee is under pressure and the central bank sells US dollars worth an amount X to commercial banks.

1. Banks pay for the dollars with rupees. Rupee liquidity in the banking system falls by X, and foreign reserves fall by X.
2. Less liquidity pushes short-term interest rates up, which the bank may not want.
3. To sterilize, the bank injects rupees worth X through open market operations, for example a reverse repo or buying government securities.
4. Result: reserves are lower by X, domestic assets are higher by X, and the money base is back where it started.

The reverse case: when the bank buys dollars to build reserves, it adds rupees. It sterilizes by draining them, for example by selling securities or running mop-up operations.

Edge cases experienced readers should know

• Automatic sterilization. When a central bank targets an overnight rate inside an interest rate corridor, its daily liquidity operations tend to offset intervention flows without a separate decision.
• Cost. Draining liquidity means paying domestic interest. If that rate is above the yield on foreign reserves, sterilization has a running cost to the central bank.
• Other tools. Sterilization can also run through reserve requirements, central bank bills or FX swaps.
• Limited effect. With open capital flows, sterilized intervention leaves interest rates mostly unchanged. Its effect on the exchange rate then depends on the signalling and portfolio-balance channels, and research finds it is often temporary.

Where the term appears

• Central bank statements and balance sheet data. These show NFA and NDA, open market operations and reserve changes. In Pakistan, policy decisions come from the State Bank of Pakistan. A recent example from our sources: SBP policy rate raised by 50 bps to 12% with effect from 27.10.2026 (MPC).
• IMF and rating agency reports. These discuss reserve buildup and how much of it was sterilized.
• News. Headlines such as "central bank buys dollars from the interbank market" or "liquidity injection via OMO" describe the two halves of the same process.
• Trading platforms. You will not see the term as an indicator. It shows up in economic calendar notes and market commentary.

Intervention news can move currency pairs sharply. Leveraged forex and CFD trading can lose money fast. See risk management.

Related terms

• Basis point
• Currency appreciation and currency depreciation
• Devaluation and revaluation
• Crawling peg and currency board
• Capital and financial account
• Covered interest parity
• Bond auction
• Fundamental analysis
• Trading glossary

Frequent questions

What does sterilized intervention mean in simple words?

The central bank trades foreign currency to influence the exchange rate, then adds or removes local money so the overall money supply does not change.

What is the difference between sterilized and unsterilized intervention?

Unsterilized intervention changes the money supply and interest rates. Sterilized intervention keeps them roughly the same.

Why do central banks sterilize?

To pursue an exchange rate goal without changing their inflation or interest rate stance.

Does sterilized intervention always work?

No. Without a change in interest rates, its effect on the currency is often small or short-lived. This is especially true when capital moves freely.