QuantCalc Retirement Engine

QuantCalc Retirement Engine — Claude plugin

Gives Claude the retirement engine and the federal and state tax engines behind quantcalc.app, so a projection or a 2026 tax figure is computed rather than estimated.

A language model cannot run thousands of correlated return paths against a spending plan and get the odds right. It can ask something that can.

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Install

Install from the Claude plugin directory. The plugin installs switched off, and you enable it when you want it. Step-by-step instructions are in SETUP.md. To use the server without the plugin, add it as a custom connector:

https://mcp.quantcalc.app

What's in the plugin

• Connector: the hosted QuantCalc engine over streamable HTTP. No account or sign-in is needed.
• Skill `retirement-projections`: loads when a plan, withdrawal rate or success rate comes up. It keeps the assumptions attached to every number and flags differences that fall inside the margin of error.
• Skill `tax-calculations`: loads when a 2026 tax question comes up — a return, a paycheck, an RMD, a Roth conversion, IRMAA, capital gains, estimated payments or the ACA credit. It maps each question to the tool that computes it and keeps the defaults and the not-modelled items with the figure.
• Skill `setup`: connection steps, what a licence key changes, and troubleshooting.

Tools

Twenty-two tools. "Free" means the tool computes without a licence key; "Licence" means it needs a connected QuantCalc PRO licence or Tax Season Pass (PRO only where stated).

Since server 1.10.0 the connector lists tools by what the session can run. With no key connected it lists the eleven that compute without one: the five free projection tools, calculate_rmd, irmaa_check, retirement_plan_deferral_savings, ira_deduction_and_roth_limit, standard_deduction_vs_itemizing and aca_premium_tax_credit (coverage year 2027). A tool that is free in part is listed with the inputs its free part takes. With a key connected it lists all twenty-two.

Retirement projections

2026 tax returns and calculators

Since server 1.9.0 these tools take tax_year 2027, on the IRS's published 2027 amounts (Rev. Proc. 2026-35): calculate_2026_income_tax, pretax_contribution_savings, roth_conversion_tax_cost, qcd_tax_savings, social_security_taxable_amount, capital_gains_tax, standard_deduction_vs_itemizing, the tax on an RMD in calculate_rmd, and business_deduction_tax_savings for a dollar expense (federal only; the 2027 mileage rate is not published). A state line in a 2027 result stays on that state's 2026 rules and is labelled so. The 2027 contribution limits and IRA income ranges are projections until the IRS publishes its limits notice, and are labelled as projections. estimate_2026_tax_return, state_tax_in_every_state and estimated_tax_payments_2026 are 2026 only.

All twenty-two are read-only: they compute and return, and change nothing. Inputs are not kept after the run, except that a failed request is kept for two days to diagnose it.

What comes back with every number

A success rate is meaningless without its assumptions, and a summary will drop a caveat it was not handed explicitly. So each result states:

• the return model that actually ran — reported by the engine, not by the request;
• the number of paths and the real trial count behind the rate;
• the income it assumed, including when it assumed none;
• whether a correlation matrix had to be adjusted before running;
• a plain warning when a run is not precise enough to show a client;
• for the tax-aware tool: the spending convention (after tax — what the household keeps), every default assumed for an input that was not given, and the tax items the engine does not model.
• for the every-state ranking: the engine versions, the federal tax it used for every state, the county taxes the state figures include, and every default assumed (spouse's age, how a couple's income is split, a private pension).
• for the 2026 tax calculators: every default assumed for an input that was not given, what is projected rather than published (the 2027 and 2028 IRMAA tables, a 2027 tax year), and that the figure is an estimate, not tax advice.

Licence key

Optional. Without one, projections run at 2,000 paths (the 95% interval around a success rate is about ±1.5 points) and the tax-aware tool returns the first retirement year of its year-by-year schedule. A QuantCalc PRO key raises that to 10,000 paths (about ±0.7) and returns the full schedule. The tax engine inside the projections — withdrawal order, Roth conversions, state tax — needs no key.

The 2026 tax tools run on QuantCalc's licensed federal and state tax APIs and need a PRO or Tax Seas