The chart shows how duration changes as yield rises. X-axis shows the prevailing yield ranging from 1% to 8%, and Y-axis shows the duration ranging from 7 years to 16 years. Duration remains close to constant (at 8 years) until the yield is between 1% and 4%, rises dramatically from 8.5 years to 15 years when the yield rises from 4% to 6%, and plateaus around 16 years beyond 6% in yield.
Duration of a 5% callable bond
When the yield is in the high single digits, the market prices in effectively 0% probability of the call, resulting in the longest possible duration, 16 years.
When the yield is sufficiently lower than the coupon, the market effectively prices in a 100% probability of the call, resulting in the shortest possible duration, 8 years.