Data Governance & Methodology
Methodology — demographic model: gross payments and contributions are no longer two independently-fitted growth rates. Each is now (headcount from the population pyramid) × (price escalator). Pensioner headcount and active-member headcount for FY2025-26 onward scale directly off the same population-by-age model shown on the left — pensioners scale with the 65+ cohort, active members scale with the 20–64 working-age cohort — so if the pyramid shows the working-age pool flattening as the 45-64 wave ages through, active-member growth (and so contribution growth) flattens with it, rather than being assumed to escalate indefinitely. Price escalators are Hymans Robertson's long-term actuarial assumptions endorsed by the PSPA Board (25 May 2020): benefit indexation 2.0%/yr, salary growth 4.0%/yr. Base year FY2024-25 is confirmed from the PSPA Annual Report (gross £143.3m, contributions £95.2m, net £48.1m; active 10,854 / pensioners 6,835). Population held flat beyond 2051 (the model's last demographic snapshot) — years beyond that are a flatter, more conservative extension than a true bulge-driven scenario would show.
Population pyramid — no assumed mortality curve, no invented migration figure: the 2021 baseline (17 age bands, 0-4 through an open-ended 80+) is the real IoM Cabinet Office Census 2021 Table 2.1. Every 5-year step after that ages the pyramid forward using cohort transition rates derived empirically from the Island's own real census history — comparing the actual population in each age band at one census against the actual population one band older at the next census, across all four available censuses (1996, 2001, 2011, 2021; source: observatory.coalfinch.com's Demographics Explorer pipeline, itself sourced to IoM Cabinet Office Census Tables 2.1-2.3, 1996 Table 3, 2001 Table 6). Because a census snapshot can't separate "died" from "emigrated" from "never arrived," these rates are net of mortality and migration exactly as the Island experienced it over 1996-2021 — which is why no separate migration figure is layered on top (that would double-count it). New births per step are the average of the three most recent confirmed years (2022-2024: 580, 609, 574 — Population Report 2025), replacing what was previously a flat, undocumented guess. One data-quality note: the Demographics Explorer's percentage-based pyramid series and the Cabinet Office's absolute 2021 headcount table don't agree perfectly in level (a discrepancy of 15-20%+ in some bands, despite both citing the same ultimate census). This model resolves that by anchoring absolute headcounts to the Cabinet Office table (independently verified) while taking only the ratios between census years from the Demographics Explorer series — ratios are far more robust to a systematic scaling difference between two sources than absolute levels would be. Caveat: net migration in 2022-2024 ran above the 1996-2021 long-run average baked into these rates (548 → 600 → 651/yr, per Population Report 2025), so this model may understate near-term working-age growth if that recent trend continues. No official Isle of Man population projection exists to check this against — Statistics IoM's own 2025 report contains no projection or mortality table, and this is confirmed independently in the Demographics Explorer's own sourcing notes.
Switch scenarios above to see how migration changes this chart: the pills at the top of the page toggle between four migration paths run off this real cohort-transition model — the same one behind observatory.coalfinch.com's Demographics Explorer, plus one added specifically for this page. Historical trend (1996-2021 average rates, no migration adjustment) is the plainest: IoM's total population actually declines slightly, 84,069 → 80,764 by 2041, so active-member growth — and contribution growth — is fairly muted. Actuarial Assumptions (300/yr) reproduces the migration assumption baked into the State Pension tab's own GAD-sourced NI Fund projection (2023-GD-0005), so the two tabs can be compared on a common footing — GAD doesn't publish its own age breakdown, so the age distribution is this model's, not GAD's; lands at 87,163 by 2041. Recent trend (adding the confirmed 2022-2024 average net migration, 600/yr) lands at 93,558 by 2041 and independently matches the Government's own 2024 OAHN housing-need evidence base almost exactly. Target — "Our Island, Our Future" (2022) back-solves the migration rate behind the 100,000-by-2037 ambition and reaches 103,963 by 2041. Moving from Historical up through Target, active-member headcount and contributions grow progressively faster, and the funding gap on this chart closes faster too — but pensioner headcount grows faster as well, so the net effect on the gap is smaller than the contribution growth alone would suggest. None of the four is presented as "the" forecast; Actuarial Assumptions (300/yr) is the default shown on page load because it's the same migration assumption the real State Pension tab is built on, not because it's the most likely outcome.
Cash terms, not constant prices: every £m figure on this chart is in cash (nominal) terms — the year each pound is actually paid in — not deflated to a constant base year, same convention as the GAD's own State Pension figures on the other tab. So the upward slope you see is two effects stacked together: price (2%/yr benefit indexation, 4%/yr salary growth — both nominal, not real-terms) and volume (headcount, from the population pyramid).
Employer/member split — real or historically-derived only: years FY2018-19, FY2019-20, FY2021-22, FY2022-23 and FY2023-24 use the Isle of Man Government Unified Scheme 2011's own real employer/member contribution figures from its Annual Reports and Accounts (66.0-72.5% employer share; FY2018-19's 72.5% is shown as reported even though it's excluded from the forward-looking average as an outlier). Years without a sourced figure (FY2016-17, FY2017-18, FY2020-21, FY2024-25, and every projected year) use 66.2% employer share — the average of the three most recent real years (FY2021-22 to FY2023-24) — flagged as a historically-derived estimate, not an assumption invented for this chart. Unified is the largest of PSPA's five schemes but not the only one, and this ratio is applied to the whole PSPA-wide total since scheme-by-scheme splits for Teachers/Police/Judicial/Manual Workers aren't available. Red is "Funded by GRA" only for real historic years (FY2022-23 onward, when PSEPR ran dry) — for every projected year the same red segment is relabelled "Funding gap" because it hasn't actually been drawn from General Revenue yet, it's simply the calculated shortfall if nothing changes.