A retirement planner that shows its working
Glidepath is a free, open-source desktop app for planning retirement and investments, built UK-first. Every number in your plan is a fact you stated, a decision you made, or an assumption the app defaulted — always inspectable, never silently guessed.
All data stays local on your machine; nothing is transmitted.
Facts, decisions, assumptions
The core principle: you can always see where a number came from. A provenance view lists everything each projection used — with its value, source, date, and whether it was defaulted or overridden.
What you stated
Your date of birth, salary, balances, pension forecasts. Entered by you, dated, and never altered by the app.
What you chose
Retirement age, contributions, planned outflows. The only fields a what-if scenario is allowed to override.
What was estimated
Returns, inflation, longevity, uprating policy. Each carries its value, source and date — and you can override any of them.
What it models
Single person, UK, from verified 2026/27 tax-year data files — policy figures are never hardcoded.
Tax wrappers
Workplace DC, SIPP, S&S ISA, LISA, GIA and cash — with UK contribution-relief mechanics and dividend and savings taxation.
DB & state pension
Deferred or actively accruing CARE-style defined benefit pensions with revaluation, early/late factors and commutation; state pension from your official DWP forecast, including deferral.
UK tax, verified
rUK and Scottish income tax, pension annual allowance with taper and MPAA, and the lump-sum allowance — all from dated, sourced data files.
Monte Carlo projection
Deterministic or Monte Carlo runs: success rate, probability of ruin, ending-pot percentiles and chart bands — reproducible from a seed, with a de-risking glide path and tax-aware decumulation.
“When can I retire?”
A solver for the earliest retirement age that sustains a target income — a replacement rate you choose, met deterministically or at a Monte Carlo success target.
Historical backtesting
Replays your plan over every rolling window of world market history since 1900 — sequence-of-returns risk that independent Monte Carlo draws miss.
Scenarios
Named what-ifs over your decisions and assumptions, compared side-by-side. Plans are saved as a local JSON file you own.
Local and private
A desktop app, not a web service. Your plan lives in a file wherever you choose, and nothing ever leaves your machine.
A closer look
All screenshots show example data, not anyone's real finances.
Get started
Requires only uv, which manages the Python toolchain for you.
$ git clone https://github.com/williajm/glidepath.git
$ cd glidepath
$ uv run glidepath # first run installs the locked dependencies
The app launches with an example plan already projected, so every tab has
something to show — replace its values with your own facts, or clear
the form and start blank. Save your plan from the File menu as a
.glidepath.json file stored wherever you
choose; the next launch reopens it automatically.