cash-flow matching

Cash-flow matching is the most literal way to back a set of promises: for every payment you must make, line up an asset that pays you exactly the same amount at exactly the same time. If you owe 100 next June, hold something that delivers 100 next June. Do this for every future obligation and the money to pay each one is already on its way before the bill arrives. There is nothing to forecast and nothing to sell at an awkward moment.

In practice you build a portfolio of bonds whose coupons and maturities, added up date by date, mirror the liability cash flows. Suppose you owe 50 in year 1, 50 in year 2, and 1,050 in year 3. A 3-year bond paying a 50 coupon each year plus 1,000 at maturity matches the lot perfectly. When the schedules line up like this, interest-rate movements become almost irrelevant: it does not matter what happens to bond prices in the meantime, because you are holding each bond to deliver the cash you need on the day you need it. You never have to sell early at a loss, and you never have to reinvest at an unknown rate.

Why it matters: cash-flow matching gives the strongest protection of any ALM technique — it neutralizes both interest-rate risk and reinvestment risk at the same time, because nothing is sold and nothing is reinvested. Its drawbacks are equally clear. It is rigid and often expensive: real liabilities (claims, lapses, longevity) are uncertain in both amount and timing, so a perfect match is impossible for most insurance business, and the bonds needed to match very long or oddly-timed payments may not exist or may be costly. For these reasons cash-flow matching is used where the liabilities are fixed and certain — a closed block of annuities, a defined pension payout — while immunization and broader ALM handle the messier, uncertain rest.