First, What Is a Bond?
Think of a bond as a simple IOU. When you buy a bond, you are lending money to an entity, which could be a corporation or a government. In return for this loan, the issuer promises to pay you periodic interest payments, known as the 'coupon', over a set
period. At the end of that period, when the bond 'matures', the issuer repays your original loan amount, called the 'principal' or 'face value'. Because they offer predictable payments, bonds are often seen as a cornerstone for steady income in an investment portfolio.
The Seesaw Effect
The relationship between bond prices and interest rates is like a seesaw: when one side goes up, the other must come down. So, when overall market interest rates rise, the market price of existing bonds tends to fall. Conversely, when market interest rates fall, the price of existing bonds tends to rise. This principle is fundamental to the bond market, but the real question is, why does it happen?
The Logic of Attraction
The reason for this inverse relationship lies in competition and attractiveness. Imagine you own a bond that you bought for ₹10,000 and it pays a fixed 6% coupon (₹600 per year). Now, let's say the broader market interest rates rise, and a new, similar bond is issued that pays 7%. A new investor with ₹10,000 can now earn ₹700 a year. Suddenly, your 6% bond looks less attractive. Why would anyone pay you the full ₹10,000 for your bond that pays ₹600, when they could buy a new bond for the same price and earn ₹700? To make your older, lower-paying bond appealing to a buyer, you have to sell it for a lower price—a discount. This price drop ensures that the new owner's actual return, or 'yield', is competitive with the new 7% bonds on the market.
Coupon Rate vs. Yield
This brings up a crucial distinction: the coupon rate versus the yield. A bond's coupon rate is fixed—it's the interest payment promised when the bond was first issued. The yield, however, is the actual return an investor gets based on the price they pay for the bond. If you buy a bond at a discount (below its face value), your yield will be higher than the coupon rate. If you buy it at a premium (above face value) because market rates have fallen, your yield will be lower. This concept of yield is what allows bonds with different coupon rates to be traded fairly in a changing market.
The Role of the Central Bank
Market interest rates don't change in a vacuum. In India, the Reserve Bank of India (RBI) is the key player. Through its Monetary Policy Committee, the RBI sets the repo rate, which is the rate at which it lends to commercial banks. This decision influences borrowing costs across the entire economy. When the RBI raises rates to control inflation or cool an overheating economy, it directly leads to new bonds being issued with higher yields, triggering the price drop in older bonds. Conversely, when the RBI cuts rates to stimulate growth, older bonds with higher coupons become more valuable.
What This Means for Investors
Understanding this relationship is crucial for any investor. If you plan to hold a bond until it matures, the day-to-day price fluctuations are less of a concern because you will get the full principal back at the end (barring a default by the issuer). However, if you think you might need to sell your bond before it matures, you are exposed to interest rate risk. If rates have risen, you may have to sell at a loss. This is especially true for longer-term bonds, which are more sensitive to interest rate changes. For investors in bond mutual funds, this dynamic directly affects the fund's daily net asset value (NAV).
