What the number of years actually names. A twenty-year level term policy guarantees the premium for twenty years. It does not follow that the contract ends in year twenty-one, and NAIC's Life Insurance Buyer's Guide is direct that most term coverage can be continued: "Most term life insurance coverage can be continued ('renewed') at the end of the term, even if your health has changed. If you renew a term policy, the new premiums are higher. Ask what the premiums will be before you renew the policy. Also ask if you'll lose the right to renew the policy at a certain age. A nonrenewable term policy can't be continued. You'll have to apply for a new policy if you still want coverage." Washington's Office of the Insurance Commissioner adds the mechanism: on a renewable policy "you may buy it for another term at a rate guaranteed in the policy, without providing health information and some other proof of insurability," but "the renewed policy will usually cost more. Over time, it may be too costly to renew." So the useful questions at purchase are three: is it renewable, at what rate, and up to what age.
Why the renewal price jumps so far, which is the part that surprises people. The risk of dying rises every year, so the true annual cost of a death benefit rises every year. A level premium does not change that; it averages it. Over a twenty-year period the buyer pays more than the current cost of the coverage in the early years and less in the later ones, and the early overpayment is what funds the later shortfall. At the end of the period that prefunding is spent. Whatever the contract charges next has to cover the cost of insuring the insured at their attained age with nothing set aside against it, which is why a renewal rate can be a multiple of the expiring premium rather than a modest step up. The same arithmetic explains why buying a longer level period costs more per year at the outset: more of the expensive later years are inside the average.
Level does not automatically mean guaranteed, and the disclosure rule is the place to check. NAIC's disclosure model defines "nonguaranteed elements" at section 4.D to include "the premiums, credited interest rates (including any bonus), benefits, values, non-interest based credits, charges or elements of formulas used to determine any of these, that are subject to company discretion and are not guaranteed at issue." Premiums are the first item on that list. The model then requires at section 7.D that "any reference to nonguaranteed elements shall include a statement that the item is not guaranteed and is based on the company's current scale of nonguaranteed elements." A contract can therefore quote a current premium below a higher guaranteed maximum, and the two numbers are both in the policy. Where the model has been adopted, the quoted figure has to be labeled; the buyer's job is to find the guaranteed maximum and decide whether the coverage is affordable at that number rather than at the illustrated one. NAIC models are not law until a state enacts them, and the disclosure model does not apply to group life, credit life or variable policies at all.
Where it sits among the other patterns. Annually renewable term charges a premium that rises every year, which is the underlying cost stated honestly and is cheapest in year one and unaffordable eventually. Decreasing term holds the premium level while the death benefit falls, which suits a shrinking debt and nothing else. Return of premium keeps both level and refunds the premiums if the insured survives, at a substantially higher price. Level term holds both steady and refunds nothing, which is why it delivers the most death benefit per premium dollar of the four. How much coverage to buy, and whether to stagger several policies with different end dates, are questions about the coverage rather than about the pattern, and belong with the general term material.