How the bands are calculated

Forrester's TEI methodology has four quadrants — Benefits, Costs, Flexibility, Risk. We use the benefits + costs lines directly and apply explicit risk adjustments to the productivity benefits. The flexibility line (optionality value of the investment) is excluded because it requires assumptions about future use cases we'd rather not invent.

8 primary Forrester TEI studies verified today: Microsoft Dynamics 365 ERP TEI, Microsoft 365 Copilot TEI, Slack for Marketing TEI, Salesforce for Manufacturing TEI, Google Workspace Forrester TEI, Rippling Forrester TEI, Mixpanel TEI (April 2026), Salesloft Forrester TEI. All ROI claims pulled directly from the executive summaries.

Adoption (50% / 80% / 95%) — % of total seat population actually using the SaaS as intended by Y2 steady state. Vendor calcs assume 95%+; reality across the eight verified TEIs averages ~75%.

Recapture (30% / 50% / 80%) — % of saved time that actually converts to dollar-value savings. Sales role: 25-35% (low — saved time absorbs into pipeline expansion). Back-office: 50-75% (high — saved time directly reduces FTE need). Knowledge worker: 30-60% (mid). Forrester's house standard is 50% — half of what vendor calcs assume.

Accuracy (85% / 95% / 98%) — % of productivity gain that survives quality control without requiring rework. P10 accounts for material rework; P90 assumes mature processes and good vendor implementation.

This is the most important methodology difference between this calculator and every vendor calculator. Vendor calculators implicitly assume that 100% of saved time converts to dollar value — every minute saved becomes a minute available for revenue-generating or cost-reducing work. Forrester's own house standard, used across all eight verified TEI studies, is 50%. Half the saved time gets absorbed by Parkinson's law, mid-cycle context-switching, or just longer breaks.

Multiplying it through: a vendor calculator showing 400% ROI typically converts to ~150-200% ROI when you apply Forrester's own recapture rule. Add P10 sensitivity and you're looking at break-even-to-modest-positive on the pessimistic end — which is what actually happens to most SaaS projects in Y1.

SaaS vendors gate SSO (the security feature most enterprises require) behind higher pricing tiers. The median premium across the 38 SaaS vendors with verified public pricing on ssopricing.com is +147%. That means a $20/seat tier becomes $50/seat for the SSO tier on the median vendor.

The calculator pulls this default. Users can override per their actual vendor — HubSpot is +650%, Asana is quote-only, GitLab is included (0% premium). The point: most SaaS ROI calculators model the cheapest published tier; the buying reality often forces the SSO tier.

Three-year horizon, 10% discount rate (Forrester standard), explicit Y2 price escalation by category (5-25%), Y3 same escalation applied. No terminal value because most SaaS contracts re-negotiate at 36 months. Churn is not modelled at this layer — the calculator assumes the SaaS is retained through Y3.

Every per-category productivity benchmark in the calculator comes from a vendor-commissioned Forrester TEI study. Flag is explicit in the category benchmark table. Independent baselines for sanity-check: McKinsey's average AI user saves 5.4% of work hours (~2.2 hr/wk), St. Louis Fed measured +1.1% US productivity gain from GenAI by H2 2024. Both are materially lower than per-vendor TEI numbers.

Forrester TEI references re-verified quarterly. Category benchmarks re-checked when major TEI studies are republished (Microsoft, Google, Salesforce, Rippling). Multi-year SaaS contract data refreshed against SaaStr / Pavilion / Stax Bill benchmarks annually. Pre-deploy CI gate refuses to publish data >90 days stale.

Soft benefits (employee satisfaction, capacity for high-value work, faster customer response). They're real but not measurable in £/$ without large assumptions. Including them is what gets vendor calculators above 400% ROI; excluding them is what keeps this site honest.

Risk reduction (security, compliance, business continuity). Genuine value, but the framing turns into "imagined avoided losses" that's ungrounded. We'll add a separate risk-reduction-value calculator if there's a defensible methodology.

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Stale TEI reference, broken source URL, methodology disagreement you can defend with data? Email hello@digitalsignet.com with the source URL. Updates land within seven days.