The industry sells the two grades as one phrase, and the phrase is a term of art. NAIC's model for supplementary health and disability income protection names three permitted labels together, "noncancellable", "guaranteed renewable", and "noncancellable and guaranteed renewable", and applies the same standard to the first and the third. So a policy described as noncancellable and guaranteed renewable is not carrying two separate promises stapled together. It is the stricter grade, written out in full, and it is the form a disability income proposal will usually use. Reading the compound as an upgrade over plain "noncancellable" is reading something the regulation does not say.
Where the labels come from matters, because neither model reaches every contract. NAIC's Long-Term Care Insurance Model Regulation supplies the definitions quoted above for long-term care insurance, and its section 6A(1) restricts an individual long-term care policy to those two renewal provisions and no others. Its model regulation for supplementary health insurance supplies a parallel set for individual and group policies providing hospital or other fixed indemnity, accident-only, specified accident, specified disease, limited benefit health and disability income protection, and that regulation expressly does not apply to long-term care, Medicare supplement or TRICARE supplement coverage. Both define the labels for individual policies. And neither is law anywhere until a state enacts it, which states do with variations, so the operative text is always the state's insurance code and the policy written under it. That code often reinforces the no-unilateral-change half of both grades independently of the labels. California, for one, provides that after issuance "a disability policy shall not be amended, changed, limited, altered, or restricted by any means other than rider upon a separate piece of paper", which forces any change onto a separate document the policyholder receives rather than into the small print of a renewal notice.
The mandated consumer wording carries a carve-out that is easy to drop, and it is the one circumstance in which a noncancelable premium legitimately rises. NAIC's prescribed outline of coverage requires a noncancellable long-term care policy to tell the buyer that the company "cannot change any of the terms of your policy on its own and cannot change the premium you currently pay." Then it adds: "However, if your policy contains an inflation protection feature where you choose to increase your benefits, [Company Name] may increase your premium at that time for those additional benefits." The premium is frozen against the insurer's unilateral action, not against the policyholder's own election to buy more coverage. A quotation of the first sentence without the second overstates the guarantee.
What the stricter grade costs, and why the comparison is harder than it looks. An insurer that cannot reprice has to charge enough at issue to absorb the risk it can no longer pass on, so a noncancelable contract starts more expensive than a guaranteed renewable one with the same benefits. It is also underwritten more carefully, and on disability income coverage the availability of the grade commonly narrows with occupation class, which is a limit on who can buy it rather than on what it does. The comparison a buyer is making is therefore between a known higher number and an unknown lower one, over a horizon measured in decades. Neither answer is right in the abstract. What is worth saying plainly is that the two quotes are not like for like, and a proposal that presents them as competing prices for the same product is presenting a comparison the contracts do not support.
The label sits in a family of three, and the third member is not a renewal provision. NAIC's model reserves "level premium" for a policy where the insurer does not have the right to change the premium. That describes a premium pattern rather than a renewal right, and a policy can carry a level premium schedule the insurer nonetheless retains the right to revise. On a genuinely noncancelable contract the two properties coincide, which is exactly why the labels are so easily confused, and why the renewability caption on the first page of the policy is the thing to read rather than the illustration.