The reference rate which is used to calculate the premium that a bond buyer will pay. Adding a spread to a reference rate is one method to value a bond. The spread can be calculated with respect to a benchmark, prominently the government bond rate, or the swap rate of an identical maturity. The bond price, according to this method, can be a specific number of basis points (bps) over the mid-swap.

The mid-swap is the average of bid and ask swap rates. As such, the bond price is made up of “n” basis points in addition to the interest rate offered by the swap market. Swap markets constitute an important source for medium and long-term interest rates. For example, a bond issue of USD 500 million, maturing in five years, can be priced at 287 basis points over mid-swaps.

Generally speaking, mid-swap is the price calculated as the midpoint between the bid and offer prices (buy and sell prices) on currency or interest rate transactions (swaps).