key rate duration
Key rate duration measures how much a bond's price will move if interest rates change at one specific maturity point, rather than shifting everywhere at once.
In plain English
Uncle Femi retired last year and put a chunk of his gratuity into a mix of government bonds, some maturing in two years, some in ten, some in twenty. His broker, a young woman named Ada, called him one afternoon with news that made him uneasy. The Central Bank had signalled it might raise short term rates soon, but leave the long end alone. Uncle Femi asked her plainly, 'So which of my bonds will suffer?'
This is exactly what key rate duration answers. Ordinary duration tells you how sensitive a bond is if interest rates move by the same amount across all maturities, a neat but unrealistic assumption. In real life, rates on two year debt can rise while ten year debt barely moves, or the other way round. Key rate duration breaks a bond's sensitivity into pieces, one for each maturity point along the yield curve, so you can see exactly where the pain or the gain will come from.
Ada explained it to Uncle Femi like this. His two year bond had a high key rate duration at the two year point and almost none anywhere else, so if short rates rose, that bond alone would take the hit. His twenty year bond barely reacted to short rate moves but would swing hard if long term rates shifted. His money was not equally exposed everywhere, it was exposed in specific spots.
Someone in London managing a small pension pot invested through a bond fund faces the same question when the Bank of England hints at a rate move. A fund holding bonds across many maturities will not react uniformly, some slices will wobble and others will sit calm.
Fund managers use key rate duration to build portfolios that are protected against particular shocks, more than rate changes in general. It lets them say, quite precisely, 'I am not worried about the ten year point, but the five year point could hurt me.'
A bond fund holds ₦50,000,000 in mixed maturities. Its key rate duration at the five year point is 3.2, meaning a 1% rise in five year rates alone would drop that portion's value by about 3.2%, roughly ₦1,600,000, even if rates elsewhere stay unchanged.
Questions people ask
How is key rate duration different from ordinary duration?
Ordinary duration assumes rates move by the same amount at every maturity, which rarely happens. Key rate duration splits that sensitivity into separate figures for each maturity point, so you see precisely where a bond or portfolio is exposed.
Why would an everyday investor care about this?
If you hold bonds or a bond fund, knowing which maturities react to which rate moves helps you understand what news to watch. A Nigerian holding short dated treasury bills should watch different signals than one holding long dated FGN bonds.
Can key rate duration be negative?
Yes, in some cases, particularly with bonds that have unusual features like call options, the sensitivity at a given maturity point can work in the opposite direction, though this is less common with straightforward government bonds.
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