Project a government's debt-to-GDP ratio under rate and growth uncertainty - a full Debt Sustainability Analysis in a browser tab.
See it run - a worked example, 100% in this browser tab
The problem
Public-finance and treasury teams run debt sustainability analysis in spreadsheets or on licensed platforms, and the projections rarely show their own sampling error or flag where the arithmetic stops being trustworthy.
The local-first solution
This plugin projects the debt-to-GDP ratio forward with the standard IMF debt-dynamics identity, driving the interest rate with an exact-discretization Vasicek process and nominal growth with an AR(1), over a seeded Monte-Carlo ensemble. It builds the fan chart, the probability the ratio rises above its start or a policy threshold, and the expected interest bill - and it self-validates the simulator against the Vasicek closed-form moments, reporting the Monte-Carlo standard error. Every projected year carries a GeoNum drift verdict.
What it does
IMF debt-dynamics recursion d' = d(1+r)/(1+g) - pb (Escolano 2010)
Exact-discretization Vasicek interest rate and Gaussian AR(1) nominal growth
Monte-Carlo fan chart (5/25/50/75/95 percentiles of debt-to-GDP each year)
Probability the ratio rises above its start or above a policy threshold
Simulator self-validated against the Vasicek closed-form mean and variance
Monte-Carlo standard error on the terminal mean, shrinking as 1/sqrt(N)
Per-horizon GeoNum drift verdict on the projection arithmetic
Honest scope
This is a model of an uncertain future, not a forecast. A GeoNum verdict means the arithmetic of the projection is sound; it does not mean the Vasicek/AR(1) assumptions are the right model of the world. The parameters are dated assumptions you supply (no live feed); the rate is a single-rate proxy for the effective rate on the stock (real DSAs blend the legacy maturity profile). Monte-Carlo percentiles carry the sampling error shown. Not investment or policy advice.
Authorities cited
Escolano, J. "A Practical Guide to Public Debt Dynamics, Fiscal Sustainability, and Cyclical Adjustment of Budgetary Aggregates." IMF Technical Notes and Manuals 2010/02. The debt-dynamics (snowball) recursion d_{t+1}=d_t(1+r)/(1+g)-pb implemented here.
Vasicek, O. "An Equilibrium Characterization of the Term Structure." Journal of Financial Economics 1977, 5(2), 177-188. The mean-reverting short-rate process and its closed-form transition/moments used for the rate driver and the self-validation.
International Monetary Fund. "Staff Guidance Note on the Sovereign Risk and Debt Sustainability Framework for Market Access Countries." 2022. The stochastic fan-chart approach to debt-sustainability analysis this reproduces at a simplified single-rate level.
Glasserman, P. "Monte Carlo Methods in Financial Engineering." Springer, 2003. Standard reference for the ensemble estimator, its standard error, and exact SDE discretization.
Run a debt-sustainability projection
Enter your debt, rate, growth, and primary-balance assumptions and run the full ensemble in the browser - nothing is uploaded. Save the scenario to a Sandbox workspace to compare policies.