The four criteria that exempt you from ILMT.

The default expectation is that sub-capacity requires an approved measurement tool, usually ILMT. IBM does, however, recognize specific situations where a documented manual calculation is allowed instead. Buyers often hear that exemptions exist and conclude they qualify. The categories below are real, but each is narrower than it sounds, and the precise thresholds are defined in the current Passport Advantage sub-capacity terms rather than in folklore.

The recognized exemption categories

Across IBM's sub-capacity terms, manual calculation has historically been permitted where one of a small number of conditions applies. The categories below describe the shape of those exemptions. Treat the specifics as something to confirm against your current agreement, not as fixed numbers, because IBM revises the terms over time.

• Small enterprise size. Organizations below a defined headcount of employees and contractors may qualify to track sub-capacity manually rather than with a tool.
• Limited physical capacity. Environments below a defined physical processor capacity for the eligible products can fall under the manual calculation allowance.
• Technology that cannot run the tool. Where an eligible environment genuinely cannot support an approved measurement tool, IBM provides for a documented manual approach for that environment.
• Brief, recent deployments. A new eligible deployment is allowed a short grace window before the tool must be in place, which is the deployment side of the 90 day rule rather than a standing exemption.

Why the exemptions are easy to misread

Each category carries conditions that buyers tend to skip. Size and capacity thresholds are measured across the enterprise as IBM defines it, not per site, so a company that feels small can exceed a threshold once every entity is counted. The technology exemption is narrow and specific, not a general escape for any environment where the tool is inconvenient. And the grace window is temporary by design. Reading any of these too generously leaves you defending a sub-capacity claim with no tool and no qualifying exemption.

If you do qualify, document it like a tool

A valid exemption still demands evidence. Manual calculation means a documented, repeatable record of the virtual capacity for each eligible product, retained the same way a tool's reports would be, and refreshed on the same cadence. An exemption with no documentation behind it performs no better in an audit than a missing ILMT, because in both cases there is nothing to substantiate the sub-capacity number.

The safe default

For most virtualized estates the lowest risk path is still an approved tool, operated continuously. The exemptions exist for genuinely small or constrained environments, not as a way to avoid the work. Before relying on one, confirm eligibility against the current Passport Advantage sub-capacity terms, because the cost of assuming wrongly is a default to full-capacity charging.