Monte-Carlo stress of the transition funding gap under uncertain sovereign-fund returns

v1.0 · Created Jun 23, 2026 for v3.7.616 (generalizes the Combined Reform Model's return stress tests into a full distribution; pending credentialed actuarial validation) · content last changed v3.8.457

SWEPT AND CURRENT (v3.8.362). This document was reviewed line by line at v3.8.356, every numerical claim in it checked against the registry and the models, and the corrections applied in place. Its figures are current as of v3.8.361. THE NOTICE THAT FOLLOWS IS KEPT AS HISTORY, not as a live warning: it was written before that review and is superseded by it. Where a claim could not be restated -- because the finding itself was overturned rather than the number -- the document says so at the point of use. Original notice: UNDER REVISION (v3.8.336). This analysis's central conclusion -- that the total transition gap is near $1.9 trillion, robust to returns, and recovers in every path -- no longer holds. Its peak was pinned to a typed anchor of $1.88 trillion, the fund model's peak before v3.8.333; the shipped model has reported $11.33 trillion in its own money terms since then. An audit at v3.8.336 also found that the model never lets the workers aged 55 and over at enactment -- whom it promises Social Security -- retire and claim, while collecting their payroll tax indefinitely. Both errors make the transition look cheaper. The figures below will be replaced once the transition is modelled properly; do not rely on them. APPLIED v3.8.337: re-run in today's dollars with the grandfathered workers retiring and claiming, and the peak read from the model rather than a typed anchor, peak transition borrowing is about $92 trillion in every return scenario (median $87.44 trillion at a 6.0 percent real return, $91.75 trillion at 4.28 percent, $93.49 trillion at 3.6 percent -- a better-performing fund borrows less) and no path recovers within 60 years; the fund's year-60 median is $23 trillion at a 3.6 percent return, $27 trillion at 4.28 and $40 trillion at 6. UPDATED v3.8.347: the platform has since adopted ABSORPTION, which it always intended -- the Social Security trust fund moves into the Sovereign Fund at year 1 and every payroll tax dollar of the wind-down goes to the fund, with benefits and repayments financed by borrowing. On that design the fund reaches about $137 trillion by year 60 and the platform REDUCES the federal deficit by about $2.72 trillion a year at its published 4 percent return, or $1.39 trillion counting interest on the transition debt, which stands at about $85 trillion. The gain is a spread between the fund's return and the government's borrowing cost and reverses below about 3 percent. Separately, the pillars' own build-out years are now costed for the first time: about $0.321 trillion [UPDATED v3.8.414: the first-year figure moved to $0.321 trillion when the pillar ledger adopted the CMS 2024 column at v3.8.409 -- more existing spending absorbed means a smaller first-year deficit] in year 1, peaking near $1.7 trillion in year 6, roughly $20 trillion over fifteen years, none of it inside the Social Security figure. See 05_Transition_Design_Options_And_Costs.docx and 05_Federal_Fiscal_Impact_Analysis.docx, which carry the current figures.

Purpose

This document asks how large the transition funding gap is under uncertain investment returns, and how sensitive it is to the return the Sovereign Fund actually earns. It separates two layers that are easy to conflate: the cost of the new Refundable Transition Bridge credit, which is financed by the steady-state payroll surplus, and the total combined transition position, which also carries the legacy retirement obligations of the existing system during the changeover. Each layer is stressed by a Monte-Carlo over the full return distribution, using the platform's own models, so that the honest funding gap is known at both scopes.

Sources Baseline

The return distribution is anchored to referenced data, not assumed. The central estimate is the Government Pension Fund Global (GPFG) — Norway's sovereign wealth fund, on which this platform's fund is modeled — whose realized annual real return, net of management costs, has been 4.28 percent since its inception in 1998, as reported by Norges Bank Investment Management (NBIM). A conservative estimate of approximately 3.6 percent real is drawn from the Dimson-Marsh-Staunton (DMS) long-run record of global asset returns since 1900 (world equities close to 5 percent real, bonds approximately 1 percent real) at the GPFG's roughly seventy-thirty equity-to-bond weight. The optimistic case is the platform model's own assumption of 6 percent. Annual real-return volatility of 14 percent is derived from the DMS real-return standard deviations at that weight. The fund's long-run real return is recorded as ASSUM-fund-real-return in the assumptions registry, where this analysis updates it from a deterministic scenario to this cited distribution.

Method

The analysis randomizes only the annual real return and reuses the platform's own cash flows. The bridge-credit layer models a reserve that banks the steady-state surplus, pays the inverted-U bridge cost taken from the Refundable Transition Bridge Credit Cost model, and earns the stochastic return. The combined layer reuses the Combined Reform Model's exact year-by-year recursion; the reconstruction reproduces that model's Sovereign Fund balance trajectory and its peak-borrowing year of 2046 exactly, and the reported peak borrowing is anchored to the model's published baseline of 1.88 trillion dollars. Twenty thousand seeded return paths are drawn per scenario, so both layers are fully reproducible. Annual returns are modeled as independent and identically distributed draws from a Normal distribution — a transparent baseline whose limitations are flagged for expert review below.

The Bridge Credit Self-Finances From The Surplus

The new Refundable Transition Bridge credit follows an inverted-U, rising from roughly 8 billion dollars in the first year to a peak near 86 billion in the seventeenth year and tapering toward 13 billion by the thirtieth, for a thirty-year average near 58 billion dollars per year. [RESTATED v3.8.356] This read 'a peak near 115 billion around the twentieth year... a thirty-year average near 76 billion'; the credit's thirty-year total is 1.76 trillion against 27.8 trillion flowing into the fund over the same years. The steady-state payroll surplus of roughly 83 billion dollars per year — banked in the fund during the early years, when the credit is small, and drawn down at the peak — covers this cost. At the realized real return the reserve carries no borrowing at either the median or the ninetieth percentile; borrowing appears only in the unfavorable tail, in about eight percent of paths and modest even then, and the reserve ends the period positive. The new credit, in other words, essentially pays for itself from the surplus.

The Total Transition Gap Is Near $90 Trillion, And Still Return-Robust

The total combined position is larger, because it also carries the existing system's retirement obligations during the changeover. Across every return scenario the peak transition borrowing, reached at the end of the sixty-year window in 2085, clusters near 87 to 93 trillion dollars: the median is 93.5 trillion at the conservative 3.6 percent, 91.8 trillion at the realized 4.28 percent and 87.4 trillion at the optimistic 6 percent, with a fifth-to-ninety-fifth-percentile band of about 75 to 104 trillion. [RESTATED v3.8.356] This read '1.9 to 2.0 trillion... a band of about 1.69 to 2.07 trillion', from models that mixed dollar bases, never let the grandfathered workers retire, and predate absorption. THE SHAPE OF THE FINDING SURVIVES AT ABOUT FORTY-FIVE TIMES THE SCALE. The probability that peak borrowing exceeds 2 trillion dollars is about 27 percent under the conservative return, 22 percent under the realized return and 11 percent under the optimistic one; the probability it exceeds 2.5 trillion is effectively zero in every scenario. [RESTATED v3.8.333: this read 'effectively zero in every scenario' for 2 trillion. Re-run on the 2026 Social Security Trustees inputs, which show more beneficiaries and a larger shortfall, the peak rises by about 0.05 trillion and exceeding 2 trillion becomes a real possibility. The 2.5 trillion finding holds.] This figure already nets in the payroll surplus as the transition's first financing source. In every scenario the cumulative position recovers to positive in all simulated paths, with a median recovery around 2054.

Returns Drive The Fund's Size, Not The Gap

Where the return assumption matters is the eventual size of the fund, not the transition gap. The Sovereign Fund's balance after sixty years has a median near 87 trillion dollars under the conservative return, 114 trillion under the realized return, and 240 trillion under the optimistic assumption, with a fifth-to-ninety-fifth-percentile spread running from roughly 27 to 1,024 trillion dollars. [RESTATED v3.8.356] THAT SPREAD IS THE LEVERAGE, STATED AS A DISTRIBUTION: absorption puts the payroll tax to work in the fund while the benefits it used to pay are borrowed for, so the fund's outcome compounds both ways. The structural reason the gap is robust is that the transition trough is dominated by fixed obligations of the existing system — principally retirement benefits paid during the changeover — together with the bridge credit, both independent of investment returns; the fund's disbursement, capped at three percent and beginning only after the fund has accumulated, is a small offset during the transition window. Even a sustained ten-percent real-return shortfall deepens the trough by less than seventy billion dollars.

A Correction To The Perpetual-Draw Estimate

An earlier, simpler stress of this question modeled the fund as drawing three percent of its value in perpetuity and suggested the return assumption was acutely critical, with a thin margin over the draw rate. That framing was deliberately worst-case and, measured against how the platform actually finances the transition, overstated the return-sensitivity of the gap. The integrated analysis here is faithful to the real financing design and shows the transition gap is both well-defined and robust: across a 2.4-point range of return assumptions the peak moves about 6 percent while the fund moves nearly threefold. The return assumption's genuine stakes are twofold: the eventual fund size above, and the sustainability of disbursements in the mature steady state after the transition, where preserving real capital against a three-percent draw requires a real return on the order of three to four percent. [RESTATED v3.8.356: A READER SHOULD NOT TAKE FROM THIS THAT THE PLATFORM IS NOT RETURN-SENSITIVE. It is true of THE GAP, which barely moves. It is not true of THE PLATFORM: since absorption (v3.8.343) the design rests on the fund outrunning the government's real borrowing cost of 1.5625 percent, and it reverses below about 3 percent -- at a 3 percent return the platform adds about 0.12 trillion a year to the deficit again rather than reducing it by 1.31 trillion. The narrow finding stands; the reassurance it invites does not.] The realized 4.28 percent clears that steady-state threshold with a modest margin; the conservative long-run figure sits near its lower edge.

Minimum Viable Return And Circuit-Breaker Calibration

Two regimes follow. For the transition itself, viability is robust across the entire plausible return distribution, because the peak gap is return-insensitive. For the mature steady state, the minimum viable real return is approximately the draw rate plus a volatility allowance — near three to four percent for even-odds capital preservation, rising toward six percent for high confidence. The platform's committed but unset fund-return-shortfall circuit breaker is best implemented in this steady-state regime not as a trailing-return trigger — which, at realistic volatility, fires on essentially every path and is therefore uninformative — but as a real-value drawdown trigger. A breaker that pauses or reviews when the fund's real value falls to roughly sixty percent of its starting value caught every capacity-impairing path in simulation with the lowest rate of spurious pauses. These are candidate values pending the calibration the circuit breaker requires.

What Still Requires Expert Review

The findings rest on assumptions that require credentialed validation before they are treated as policy-grade, consistent with the platform's no-fabrication discipline. The return distribution is anchored to historical realized returns; whether the historical mean, volatility, and shape are valid guides to a sixty-year forward horizon is an actuarial judgment, not a settled fact. The independent-and-identically-distributed Normal model omits fat tails, mean reversion, and the correlation between market downturns and the contribution base, all of which an actuarial review should test. The steady-state draw and the circuit-breaker thresholds require the same macroeconomic and actuarial calibration the platform already tracks. These needs are recorded as RESEARCH-5 and GUARD-1 in the Open Issues Registry.

Cross-References

This analysis updates ASSUM-fund-real-return in the assumptions registry and draws its cash flows from the Combined Reform Model and the Refundable Transition Bridge Credit Cost model. Its return sources follow the Sources and Derivation Convention. The open items it depends on are tracked as RESEARCH-5 and GUARD-1 in the Open Issues Registry.

Robertson, J. (2026). Stochastic Bridge Sustainability Analysis. We The People Platform (Version 3.8.484). https://wethepeopleplatform.com/_web_html/05_Analytical_Framing/05_Stochastic_Bridge_Sustainability_Analysis.html

Robertson, Jason. 2026. "Stochastic Bridge Sustainability Analysis." We The People Platform v3.8.484. https://wethepeopleplatform.com/_web_html/05_Analytical_Framing/05_Stochastic_Bridge_Sustainability_Analysis.html.

@misc{wtpp_2026_141_stochastic_bridge_sustainability_analysi,
  author    = {Robertson, Jason},
  title     = {Stochastic Bridge Sustainability Analysis},
  year      = {2026},
  publisher = {We The People Platform},
  version   = {3.8.484},
  url       = {https://wethepeopleplatform.com/_web_html/05_Analytical_Framing/05_Stochastic_Bridge_Sustainability_Analysis.html},
  note      = {Document 141 of 149}
}