Negative Interest Rates and Currencies: How Sub-Zero Policy Affects Forex

What Are Negative Interest Rates?

Negative interest rate policy (NIRP) is a monetary-policy tool in which a central bank sets its policy rate — typically the deposit rate or reserve rate — below zero. Instead of paying interest on reserves that commercial banks hold at the central bank, the central bank charges a fee. The objective is to penalise banks for holding excess reserves and incentivise them to lend, stimulating credit creation and economic activity. For the broader framework, see Interest Rates and Forex Markets.

Negative rates are an unconventional tool, deployed when conventional rate cuts have been exhausted — when the policy rate is already at or near zero and the central bank wants to ease further. The policy pushes into territory that was once considered impossible: nominal interest rates below zero, where lenders pay borrowers and savers are penalised. The implications for banking systems, bond markets, and currencies are complex and not always intuitive.

Why Central Banks Use Negative Rates

Central banks deploy negative rates when the economy is weak, inflation is below target, and conventional rate cuts have been exhausted. The goal is to stimulate the economy through several channels: penalise banks for holding reserves (encouraging lending), weaken the currency (boosting exports and inflation), lower borrowing costs across the yield curve, and signal a strong commitment to reflation. For the framework, see Why Rate Hikes Don't Always Strengthen a Currency.

The decision to go negative is not taken lightly. It signals that conventional tools are insufficient and that the central bank is willing to experiment with extraordinary measures. The signalling channel is itself powerful: a central bank willing to go negative is signalling that it will do whatever it takes to reflate the economy — which can shift inflation expectations and the entire rate-path outlook.

Nominal vs Real Interest Rates

The distinction between nominal and real interest rates is critical for understanding NIRP's currency impact. A nominal policy rate of -0.5% with inflation expectations of 1% produces a real rate of -1.5%. A nominal policy rate of -0.5% with inflation expectations of -1% (deflation) produces a real rate of +0.5%. The real rate — not the nominal rate — is what matters for currency valuation. For the framework, see Real Yields and Currencies.

This means negative nominal rates do not automatically mean negative real rates. If inflation expectations are even more negative than the policy rate, the real rate is positive — which is contractionary, not expansionary. The central bank's goal in going negative is to produce sufficiently negative real rates to stimulate the economy. The currency impact depends on the real-rate differential, not the nominal-rate differential.

Bank Profitability, Credit Creation, and the Reversal Rate

NIRP operates through the central bank's deposit rate — the rate paid (or charged) on reserves that commercial banks hold at the central bank. When the deposit rate is negative, banks are charged a fee for holding reserves, which creates an incentive to lend rather than park funds at the central bank. However, NIRP creates a significant challenge for bank profitability. Banks earn a net interest margin — the difference between what they charge on loans and what they pay on deposits. When the deposit rate is negative, banks are charged for holding reserves, but they typically do not pass negative rates on to retail depositors (who would withdraw cash rather than pay to save). This compresses the net interest margin. For the framework, see Credit Spreads and Currencies.

The compression of bank profitability can have a paradoxical effect: instead of stimulating lending, it can reduce it. Banks with compressed margins may tighten credit standards, reduce risk-taking, and contract lending — the opposite of the intended effect. This is the core of the reversal-rate concept: the theoretical policy rate below which further cuts become counterproductive. Below the reversal rate, the damage to bank profitability exceeds the stimulus from lower rates — the net effect is tightening, not easing. The reversal rate depends on the structure of the banking system, the share of deposit funding, and the ability of banks to pass on negative rates. This explains why negative rates do not always produce the expected easing effect — if the policy rate is pushed below the reversal rate, the currency may actually strengthen as the banking system contracts credit.

Bond Yields, Yield Curves, and Carry Trades

Negative policy rates can push bond yields into negative territory. If the short-term policy rate is negative, the short end of the yield curve goes negative. If the market expects negative rates to persist, the middle of the curve may also go negative. The long end depends on inflation expectations: if inflation expectations are very low, even the 10-year yield can go negative. A negatively sloping yield curve is a powerful signal of deflation expectations and economic weakness. For the framework, see Yield Curves Explained and Bond Term Premium.

NIRP also affects carry trades by making the implementing country an attractive funding currency. Investors borrow in the negative-rate currency (being paid to borrow) and invest in higher-yielding currencies. This carry-trade activity puts selling pressure on the funding currency. However, the carry-trade channel requires not just a yield differential but also stable exchange-rate expectations. If the market expects the funding currency to appreciate, the carry trade is unattractive. The carry-trade channel operates only when the market expects the funding currency to remain stable or depreciate. For the framework, see Capital Flows and FX.

Safe-Haven Demand and Why Negative Rates Do Not Automatically Weaken

Negative-rate currencies can become funding currencies, but they can also remain strong due to safe-haven demand. The Swiss franc is the classic example: despite historically negative SNB policy rates, the CHF has often strengthened because of safe-haven inflows. Investors buy CHF not for yield but for safety — the Swiss franc's safe-haven status overrides the yield disadvantage. For the framework, see Safe-Haven Currencies and What Drives the Swiss Franc?.

Several factors can keep a currency strong despite negative rates. First, relative rates: if other central banks are easing even more aggressively, the rate differential may still favour the negative-rate currency. Second, safe-haven demand: if the currency has safe-haven status, risk-off inflows can overwhelm yield-driven outflows. Third, real rates: if inflation expectations are even lower than the nominal rate, the real rate is positive. Fourth, current-account surplus: a structural current-account surplus creates persistent demand for the currency regardless of the yield. For the framework, see Current Account and Currency Valuation.

The key insight is that FX is relative. A negative rate in one country does not determine the currency's direction in isolation — what matters is the rate relative to other countries, the real rate relative to other countries, and the non-yield factors (safe-haven, current account, growth) relative to other countries.

CHF and JPY: Historical Experience

The Swiss franc has historically remained strong despite negative SNB policy rates. The SNB implemented negative rates to discourage safe-haven inflows and cap CHF appreciation, but the safe-haven demand was so strong that the CHF remained bid even with negative rates. This demonstrates that safe-haven demand can override the yield channel. For the framework, see Swiss National Bank Guide.

The Japanese yen has historically strengthened despite low or negative yields, particularly during risk-off periods. The yen's safe-haven status, Japan's current-account surplus, and the repatriation of overseas assets during crises have driven JPY strength independent of the yield. For the framework, see Bank of Japan Guide and What Drives the Japanese Yen?.

Importantly, both the SNB's and BoJ's historical negative-rate frameworks were specific policy regimes, not necessarily current policy. Any description of these frameworks must be understood in their historical context, and the current policy must be verified against official sources. The ECB also historically deployed negative rates; see European Central Bank Guide.

Relative Rates vs Absolute Rates

The distinction between relative and absolute rates is the key to understanding NIRP's currency impact. A -0.5% policy rate is not currency-negative in isolation — what matters is the -0.5% relative to other rates. If the ECB is at -0.5% and the Fed is at 2%, the differential favours the dollar. If the ECB is at -0.5% and the SNB is at -0.75%, the differential favours the euro. The absolute level matters less than the relative level. For the framework, see Interest Rate Differentials and Policy Divergence.

This is why a central bank cutting deeper into negative territory may not weaken its currency if other central banks are cutting even more aggressively. The currency impact depends on the relative easing, not the absolute easing. A central bank that is the first to go negative may see significant currency weakness (because the relative differential widens), but a central bank that goes negative when everyone else is already negative may see little impact.

Expectations and Repricing

Markets price the expected path of rates, not just the current setting. If the market expects a central bank to exit negative rates in the future, the currency may strengthen before the actual exit — as the market prices the expected normalisation. Conversely, if the market expects deeper negative rates, the currency may weaken before the actual cut. For the framework, see Why Markets Trade Expectations.

The expectations dimension is particularly important for NIRP because the exit from negative rates is a major regime change. The market knows that negative rates cannot last forever — they are an emergency tool — and it prices the eventual exit. When the market begins to price the exit, the currency can strengthen even before the policy rate moves. The timing of the exit expectation is as important as the current rate setting. For the framework, see Forward Guidance.

Limits of NIRP and Exit Dynamics

NIRP has several limits. The reversal rate: below a certain level, further cuts damage bank profitability and contract credit. The cash constraint: at sufficiently negative rates, depositors withdraw cash (which has a zero nominal rate) rather than pay negative rates, creating a floor for retail deposits. The safe-haven override: for safe-haven currencies, negative rates may not deter inflows. The relative-rate limit: if all central banks are easing, the relative differential does not change. For the framework, see The Neutral Rate.

Exiting NIRP is a significant regime change. When a central bank raises rates from negative territory back to zero or above, it signals that the emergency is over and that the economy is normalising. This can strengthen the currency through several channels: the yield differential improves, carry trades unwind (requiring buying of the funding currency), and the normalisation signal attracts capital. The exit is typically well-telegraphed, but the actual exit can still produce sharp moves as the market reprices the entire forward curve.

Regime Dependency

NIRP's currency impact depends on the macro regime. During deflation risks, negative rates may be seen as necessary and insufficient — the currency may not weaken because the market focuses on the deflation problem, not the rate cut. During risk-off periods, safe-haven currencies with negative rates may strengthen as capital flows to safety. During risk-on periods, negative-rate currencies may weaken as carry trades build. During global easing cycles, the relative differential may not change, muting the currency impact. For the framework, see How Macro Regimes Change Forex Relationships.

Common Analytical Mistakes

• Assuming negative rates automatically weaken the currency: Relative rates, safe-haven demand, and real rates all matter. The absolute level is not the key.
• Ignoring the reversal rate: Below a certain level, further cuts become counterproductive for the banking system and may tighten credit.
• Forgetting the real-rate channel: The real rate (nominal minus inflation expectations) is what matters for currency valuation, not the nominal rate.
• Overlooking safe-haven demand: Safe-haven currencies can remain strong despite negative rates if risk-off flows dominate.
• Describing historical negative rates as current: The ECB, SNB, and BoJ historical negative-rate frameworks were specific regimes. Always verify current policy.
• Waiting for the actual exit: Markets price the expected normalisation before it happens. The currency may strengthen before rates actually rise.

Practical Framework for Traders

• Check the relative rate differential: How does the negative rate compare to other central banks? Is the differential widening or narrowing?
• Assess the real rate: What is the real rate (nominal minus inflation expectations)? Is it more or less negative than other economies?
• Consider safe-haven status: Is the currency a safe haven? Could risk-off flows override the yield channel?
• Monitor bank profitability: Is the banking system absorbing the cost, or is credit creation contracting? Are we near the reversal rate?
• Watch carry-trade positioning: Is the currency being used as a funding currency? Are carry trades building or unwinding?
• Track exit expectations: Is the market pricing an eventual exit from negative rates? When is the exit expected?
• Check the relative dimension: Does the negative-rate policy change the relative rate differential between the two currencies in your pair?

Related Reading

• Interest Rates and Forex Markets
• Real Yields and Currencies
• Carry Trades
• Swiss National Bank Guide
• European Central Bank Guide
• Bank of Japan Guide
• Safe-Haven Currencies
• Why Rate Hikes Don't Always Strengthen a Currency