Why Does Modelling Salary Changes Feel So Inconsistent in IB Maths?
Salary modelling is one of the most confusing financial contexts for IB Mathematics: Applications & Interpretation students. Unlike simple interest or fixed investments, salaries change in ways that feel irregular and unpredictable. Raises may be annual, percentage-based, capped, delayed, or combined with bonuses, which makes modelling feel inconsistent.
IB uses salary modelling to test whether students can handle realistic financial complexity, not tidy textbook growth. The difficulty lies in interpretation, not calculation.
Why Salary Growth Is Not a Simple Pattern
Many students expect salaries to follow a clean arithmetic or geometric sequence.
In reality, salaries often involve:
- Percentage raises
- Fixed bonuses
- Thresholds or caps
- Irregular timing
IB expects students to recognise that salary growth is piecewise and conditional, not uniform. Treating it as a single clean sequence often produces unrealistic results.
Why Percentage Raises Cause Confusion
Percentage raises feel similar to compound interest, but the context is different.
Students often forget that:
- Raises apply to the current salary
- Raises may stop after a certain time
- Raises may differ year to year
IB frequently penalises answers where students apply a constant growth factor without checking whether the raise structure actually remains consistent.
Why Bonuses and Caps Break Simple Models
Bonuses and salary caps disrupt sequence-based thinking.
A fixed bonus does not compound, while a percentage raise does. Salary caps introduce limits that stop growth entirely. IB expects students to adjust their model when conditions change rather than forcing a single formula across all years.
