How Central Banks Size Foreign Exchange Interventions

Summary

The document explains that a central bank defending an exchange-rate level can place a large limit order at its chosen price. It uses the Swiss National Bank’s former EUR/CHF floor as an example: a standing offer to buy euros at the floor would support the exchange rate while the order remained in place.

It also addresses how much currency an intervention requires. The amount cannot be known in advance because it depends on how strongly market participants trade against the defended level. The discussion gives no sizing formula or empirical estimate; it emphasizes uncertainty and the role of a central bank’s available reserves. A central bank with limited reserves may be more vulnerable to challenges from traders. The example describes a price guarantee only while the order is active, not a permanent guarantee that a currency will stay within a band.

Key ideas

• A central bank can defend an exchange-rate threshold by posting a large limit order at that price.
• The intervention amount depends on opposing market demand and cannot be determined with certainty beforehand.
• Limited reserves may make an intervention more vulnerable to market participants challenging the defended level.

Tags

# Central Bank intervention in forex market


# Central Bank intervention in forex market












Sometimes CB intervenes in fx market buy buying or selling currency to make it stay in some band. My question is how does Central Bank determine the size of interventions? I mean how do they know how much money they need to spend? For example buy 100m usd or 200musd?

## Answer by Chris Taylor (score 2)

https://quant.stackexchange.com/a/30840

They can simply place a (very large) limit order at the determined price level(s).

For example, when the SNB wanted to keep EUR/CHF above 1.20 they had a large buy order at 1.20 (i.e. they agreed to buy 1 EUR for 1.20 CHF) and this guarantees that the EUR/CHF rate stays above 1.20 for as long as the limit order is in place.

## Answer by dm63 (score 2)

https://quant.stackexchange.com/a/30848

They don't know how much intervention will be required to keep the currency at a given level. It depends how much other market participants want to resist the move. If the central bank is relatively weak, with limited reserves, participants may choose to challenge the intervention, for example.

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This summary was written by Stratmill's research agent from the original; it is not a copy of the source.