The rate on line is the ratio of a layer's premium to its limit. A layer of 10 million euros limit placed for 1.2 million of premium has a rate on line of 12%. It is the number the market quotes when it talks about a layer, the one compared from one renewal to the next and from one program to another, and it has one decisive advantage over every other measure: it depends on no assumption. It is read off the placement itself.
Its inverse has a name and a reputation: the payback. A 12% rate on line gives a payback of 8.3 years, read as the number of years of premium the reinsurer needs to rebuild the limit it has just paid. The market uses it as a pricing shortcut, and it is convenient: it turns an abstract percentage into a duration everyone can picture.
It must be said at once what that shortcut is not, because it is forgotten as soon as it is used. Payback is not a return period: it accounts for none of the reinsurer's expenses, none of the brokerage, none of the cost of tied-up capital, none of the investment income on premium held, and above all none of the actual probability that the layer is hit. It is a division, not a result. A reinsurer pricing on payback alone would be working without knowing whether it makes money.
The rate on line varies enormously along a program, and that variation is the structure of the market itself. A low working layer places at 40%, sometimes more, giving a payback of two and a half years: the reinsurer expects to pay often. A very high cat layer places at 2%, a payback of fifty years. Reading those two numbers side by side gives the shape of the program immediately, and a rate on line far out of line with its rank in the stack almost always signals something, an exclusion, a missing reinstatement, or an exposure nobody has understood.
Comparing two layers by their rate on line is therefore useful and fragile at the same time. It assumes everything else is comparable, which is rarely true. Two layers at the same rate on line can differ in their number of reinstatements, in the price of those reinstatements, in their definition of a loss, in the presence of an annual aggregate deductible, or in the existence of a minimum and deposit premium. The number is the same and the commitment is not.
Two corrections must be added that practitioners apply without always naming them. A quoted rate on line is sometimes gross of brokerage and sometimes net, and the gap counts in points on a low layer. And a layer carrying several free reinstatements does not commit the same annual limit as a layer with none: the premium is then usefully compared to the total limit mobilizable over the year rather than to the nominal limit, failing which the first looks expensive and the second cheap for no reason.
The right use of both quantities is therefore as an instrument of control, never of pricing. You price by burning cost on low layers and by an exposure model on high ones; you then check that the rate on line obtained is consistent with the layer's rank, with the market, and with what the same layer cost last year. A price coming out of a model that gives a hundred-year payback on a working layer says the model got it wrong, and that is exactly the service this measure is there to provide.
A 2027 catastrophe program has three layers. The first, 15 million euros excess of 10 million, is quoted at 4.8 million of premium, with three free reinstatements. The second, 25 million excess of 25 million, is quoted at 3 million, with one reinstatement payable at 100%. The third, 50 million excess of 50 million, is quoted at 1.4 million, with no reinstatement. An analyst concludes that the first layer is three times more expensive than the third and recommends cutting it. What should be said about that reading?
The rates on line come first, and they confirm the analyst's arithmetic observation: 4.8 over 15 gives 32% for the first, 3 over 25 gives 12% for the second, 1.4 over 50 gives 2.8% for the third. The ratio between the first and the third is in fact not three but eleven, so the analyst's reading is wrong in its figure before being wrong in its conclusion. A ratio of one to eleven is normal and expected: a layer starting at 10 million sees frequent events, a layer starting at 50 million is reached only by the rare one, and every sound program shows that gradation. The second flaw in the reading matters more, because it concerns what the three premiums actually buy. The first layer offers its limit four times over the year, that is 60 million mobilizable, at no extra premium; the second offers 25 million twice, the second time for a price; the third offers its 50 million once only. Set against the limit actually mobilizable, the first comes out at 8% rather than 32%, and the comparison reverses. Finally, cutting the bottom layer of a catastrophe program means raising the cedant's retention on the most frequent events, which is a risk tolerance decision and not a saving. The question to put to the board is not which of the three layers costs most per unit, but what level of annual loss the house accepts to carry itself.
- 01The rate on line is a layer's premium divided by its limit, and it is the only measure of a placement that depends on no assumption.
- 02Payback is its inverse: it says how many years of premium rebuild the limit, and nothing else.
- 03Payback is not a return period: it ignores expenses, brokerage, the cost of capital, investment income and the probability of being hit.
- 04The rate on line grades along a program, from 40% on a working layer to 2% on a cat layer: a departure from that rank almost always signals a clause.
- 05Two layers at the same rate on line do not commit the same thing: reinstatements, loss definition, annual aggregate deductible and brokerage separate them.
- 06You price by burning cost or by an exposure model, then control by rate on line. The reverse is not a method.