Before setup, define the tier rule
A tiered estimate can mean different things. One model applies a single rate to the entire quantity after a threshold; another applies different rates to successive portions. These produce different totals even when the threshold and rate labels look similar. Write the rule in words before using conditional functions or a lookup. If a customer-facing explanation cannot distinguish the two models, the formula is not ready to carry a commercial promise.
Configure an unambiguous boundary
For a hypothetical all-units model, quantities up to and including ten might use one allowance, while quantities above ten use another. Decide what happens at exactly ten and whether decimal quantities are possible. Avoid overlapping conditions that both include the boundary or leave it uncovered. The documented conditional operators support expressing choices, but they cannot resolve an ambiguous business rule. Keep inclusive and exclusive boundaries visible in the source specification and test notes.
Test the neighboring cases
Run nine, ten and eleven for a whole-item model. For fractional quantities, choose values just below and above the threshold at the precision you actually accept. Calculate expected results independently, not by copying the same formula into another location and calling matching outputs proof. Check that moving back across the threshold updates the result explanation as well as the number. A stale label can make a correct total difficult for the visitor or staff to understand.
Verify how the total changes
A threshold can create a sudden decrease or increase in an all-units model. Determine whether that is intentional and commercially explainable. Do not smooth the behavior secretly in the interface while saving a different figure. If the tier structure is too complex for a short explanation, consider a range or reviewed quote instead. Preserve the model version with the request so a future rate adjustment does not erase the basis of an earlier estimate.
Sources used for this page
These records support the facts and comparisons above. Merchant-controlled records are labelled so you can separate product claims from independent evidence.
- Advanced functions and conditional operators — Merchant documentation · help.involve.me · Merchant-controlled · checked 2026-09-23
- Formula builder test mode — Merchant documentation · help.involve.me · Merchant-controlled · checked 2026-09-23