A calculation engine for Claude, ChatGPT, and other MCP-compatible AI assistants — IRS tax tables for 2024–2026, RMDs, capital gains and AMT, Social Security claiming math, and projections you can dial from fast formulas to full Monte Carlo. Computed, never guessed.
I. The Problem
Large language models are great at conversation. They are the wrong tool for tax brackets, contribution limits, and projection math. Ask "Can I retire at 60?" and you get plausible text — not a computed answer with the IRS tables, the contribution limits, and the scenarios actually run.
FinPlan fixes that. Your AI assistant calls FinPlan's tools, gets exact numbers back, and answers you with math instead of narrative.
II. How It Works
Each capability is a typed MCP tool. Your assistant picks the right one, fills in your data, and gets exact numbers back. No prompt engineering. No screen scraping.
One interface, two methods.
Fast formula-based projections by default. Full Monte Carlo when path dependency or precision demands it — same tool call, you pick the method.
Explore 02Federal, state, capital gains, AMT.
IRS tables for 2024–2026 across all filing statuses. State income tax, capital gains rates, AMT, after-tax projection adjustments, and safe-harbor estimates.
Explore 03Every type, modeled.
401(k), traditional and Roth IRA, HSA, taxable brokerage, real estate — each with current contribution limits, asset-class rules, and tax treatment.
Explore 04Claiming math, end to end.
PIA from salary history, benefits at every claiming age 62–70, breakeven analysis, spousal and survivor benefits, and the earnings test.
Explore 05Required distributions, calculated.
Year-by-year RMD schedules per account, aggregation across IRAs, uniform and single-life tables, and shortfall penalties under SECURE 2.0.
Explore 06Probability-targeted.
Set goals by success probability, not just dollar amount. Four funding strategies, tax-advantaged routing, target-date flexibility, real-time progress.
Explore 07Returns, volatility, glide paths.
Capital market assumptions you can override. Per-account allocations, expected return + volatility math, age-based glide paths.
Explore 08Full amortization, on demand.
Monthly payments, full amortization schedules, principal-vs-interest splits at any point in the term — for any rate, term, or balance.
Explore 09Client-ready visualizations.
Projection fan charts, glide paths, scenario comparisons, allocation breakdowns, amortization curves. Renders client-side from typed chart data.
ExploreModel an ISO exercise with the AMT impact in the exercise year, cash needed at strike, qualifying vs disqualifying disposition outcomes, and the capital-gains math once the holding period clears. Compare scenarios side-by-side in a single conversation.
Explore equity toolsISO exercise
Strike × shares, FMV bargain element, cash required at exercise.
AMT impact
AMT in the exercise year, regular-tax delta, and credit recovery over future years.
Qualifying disposition
Long-term capital gain after 1yr from exercise, 2yr from grant.
Disqualifying disposition
Ordinary income on the bargain element, capital gain on the rest.
III. Different
State files are plain JSON on your local disk. No accounts. No cloud sync. No third-party data processor to vet, no terms of service to review.
Money is tracked in cents. Tax brackets come from published IRS documents. Nothing is rounded, estimated, or scraped from a blog post.
Reproducible. Auditable. Run a projection today and a year from now with the same data — identical results.
IV. Setup
FinPlan speaks the Model Context Protocol, so any MCP-compatible assistant can use the same tools. Connect in a few minutes.
Install the plugin in two commands. FinPlan loads as MCP tools plus a set of finplan-prefixed slash commands. OAuth handles auth automatically.
Setup guide$ claude plugin marketplace add bestdan/finplan-plugin $ claude plugin install finplan@finplan-plugin // then in any Claude Code session: > /finplan:setup
Closing
“Pick your assistant, paste a config, and ask a question with an answer you can show.”
— Ready when you are.
