A policy rate is the interest rate at which a country's central bank lends money to commercial banks overnight. In India, this is called the repo rate, set by the Reserve Bank of India. In the United States, the equivalent is the federal funds rate, set by the Federal Reserve. Think of it as the base price of money in an economy. When the central bank raises this rate, borrowing from it becomes more expensive for commercial banks. Those banks then typically pass on that higher cost by charging more for loans to businesses and individuals. When the central bank lowers the rate, the reverse happens: borrowing becomes cheaper, and credit tends to flow more freely through the economy.

When a central bank changes its policy rate, the effects do not stay inside the bank — they ripple outward through loans, bonds, currencies, and eventually everyday prices.

This process of a rate change working its way from the central bank through to the broader economy is called monetary policy transmission. It operates through several channels. The lending channel is the most direct: higher rates mean costlier home loans, car loans, and business credit, which can slow spending and investment. The bond market channel is also significant. When rates rise, newly issued bonds offer higher yields, which makes older bonds with lower yields less attractive, causing their prices to fall. This is why India's 10-year government bond saw sharp price movement today — a day when global uncertainty and surging crude oil prices raised concerns that inflationary pressure could complicate the RBI's rate-setting decisions. Bond prices and yields move in opposite directions, so a falling bond price means a rising yield, reflecting higher perceived risk or expectations of tighter monetary conditions.

The currency channel is another important route. Higher interest rates in a country tend to attract foreign capital seeking better returns, which can strengthen that country's currency. Conversely, when risk rises globally or when a country faces a widening import bill — as India does when crude oil prices spike — the currency can weaken, as the rupee did today. A weaker currency then feeds back into inflation by making imports more expensive, which in turn influences what the central bank may consider doing with rates in the future. Understanding these connections helps explain why a single piece of geopolitical news, such as a disruption in oil supply routes, can simultaneously move bond prices, exchange rates, and equity indices — they are all parts of the same interconnected system that policy rates help to regulate.