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How Impact calculates
Three worked examples. They are illustrative, and they are also the reference tests our calculation engine must pass before every release. The figures on this page are computed by that engine.
The core formulas
- Cost per unit at any stage = investment ÷ units at that stage.
- Blended view = total investment ÷ total units across all audiences.
- Allocated view = each audience's allocated investment ÷ that audience's units.
- Conversion from one stage to the next = later units ÷ earlier units.
- Attributable value = value × attribution share (method always shown).
- ROI = (attributable value − investment) ÷ investment. ROMI = attributable value ÷ investment.
Money is shown to two decimal places below £1,000 and to whole pounds above. Percentages to one decimal place. Calculations keep full precision; rounding happens only on screen.
Example 1 · Blended baseline
A university invests £750,000 in a year. Its research, student-recruitment and employer pages each receive 250,000 visitors: 750,000 in total. Each audience also gains 25,000 newsletter subscribers.
| Measure | Calculation | Result |
|---|---|---|
| Blended cost per visitor | £750,000 ÷ 750,000 | £1.00 |
| Each audience, equal allocation | £250,000 ÷ 250,000 | £3.00 |
| Blended cost per subscriber | £750,000 ÷ 75,000 | £10.00 |
Example 2 · Unequal allocation
The same £750,000 is allocated 50% to students, 20% to academic and 30% to employers. Fixed percentages: students 50.0%, academic 20.0%, employers 30.0%.
| Audience | Allocated | Visitors | Cost per visitor |
|---|---|---|---|
| Students | £375,000 | 400,000 | £0.94 |
| Academic | £150,000 | 150,000 | £1.00 |
| Employers | £225,000 | 200,000 | £1.13 |
Example 3 · The full student funnel
Students are allocated £375,000.
| Stage | Units | Calculation | Cost per unit |
|---|---|---|---|
| Enquiries | 12,000 | £375,000 ÷ 12,000 | £31.25 |
| Applications | 6,000 | £375,000 ÷ 6,000 | £62.50 |
| Enrolments | 900 | £375,000 ÷ 900 | £416.67 |
- Enquiry to enrolment conversion = 900 ÷ 12,000 = 7.5%.
- Student lifetime value = £15,000 net tuition × 3 years × 0.90 retention = £40,500.
- Total value = 900 × £40,500 = £36,450,000.
- With a declared marketing influence share of 10% (declared influence share (assumption)), attributable value = £3,645,000.
- ROI = 872.0% and ROMI = 9.72×, measured against the £375,000 student allocation.