Laddering means holding several term policies with different end dates instead of one large one. It exists because the cover a household needs falls over time while a single policy's benefit does not.
The need is a declining curve
Cover is bought to replace income and clear obligations. A mortgage amortises, children reach independence, and retirement savings accumulate year by year.
Each of those reduces the shortfall a death would create, so the required benefit is highest early and falls steadily from there.
A single level policy pays the same amount at the end as at the beginning, which means paying for cover that stopped being necessary years earlier.
The overpayment is modest in any one year and considerable across two or three decades of premiums.
Stacked policies approximate that curve
A ladder places several policies of different lengths side by side, so total cover steps down as each of the shorter contracts expires in turn.
The steps can be aligned with dates that are already known, such as the year a mortgage ends or the year a child finishes education.
The result approximates a declining need using instruments that are each individually level and individually simple.
Cover can also be reduced early by cancelling one contract, which is harder to do cleanly inside a single large policy.
The saving comes from the shorter contracts
Shorter term lengths cost less per dollar of cover because they contain fewer high-mortality years inside their level period.
Replacing part of one long policy with shorter ones lowers total premium across the period, provided all of them are bought while the insured is young and healthy.
The saving follows from matching duration to need rather than from any pricing trick on the insurer's side.
Multiple policies carry multiple frictions
Each contract has its own policy fee, its own minimum size and its own paperwork, and small policies are proportionally more expensive to administer.
Several policies also mean several beneficiary designations to keep current through a marriage, a divorce or a death in the family.
Below a certain benefit size the frictions can outweigh the premium saving entirely.
Three or four contracts is where most ladders stop, because each further layer adds administration faster than it removes premium.
Decreasing term is the alternative structure
A decreasing term policy reduces its benefit on a fixed schedule while holding the premium level, achieving a similar shape inside a single contract.
The reduction follows the insurer's schedule rather than the household's, which suits a mortgage more comfortably than it suits a family's changing circumstances.
Comparing a ladder with a decreasing policy is a comparison of flexibility against simplicity, and the answer depends on how predictable the declining need actually is.