When I started seriously planning for retirement, I went looking for a calculator that could model the whole picture. There are dozens of them on the open internet — and almost every one falls short of a genuinely comprehensive analysis. They tend to be built around a single person, a single scenario, and a single “average return,” treating all of your savings as one undifferentiated pot of money.
Real retirement planning isn’t like that. Most households are couples with two different ages and two Social Security decisions. Markets don’t deliver the same return every year. Some of your savings are taxable when you withdraw them and some aren’t. And the big questions — when should we retire?, will our money last? — are best answered by comparing options side by side, not one at a time.
So I worked with Claude Code and we built the tool I wished existed.
Plenty of tools do someof these. After a lot of looking, I couldn’t find a single free tool that does all of them. That gap is what this modeler is meant to fill.
The problem
Couples are an afterthought. Most calculators model a single person, or treat a spouse as a checkbox that just doubles the standard deduction.
What this tool does
You enter separate ages, income, Social Security, retirement dates, and pensions for each spouse. The projection tracks both timelines independently — including the year one spouse retires while the other keeps working.
The problem
You can only model one scenario at a time. Comparing 'retire at 62' against 'retire at 65' means running the numbers twice and holding them in your head.
What this tool does
Run up to three scenarios side by side — different retirement ages, claiming ages, return assumptions, spending, or states. Every chart and table updates instantly as you adjust inputs.
The problem
A single 'average return' hides the biggest risk in retirement: a bad market early on, while you're drawing down, can sink a plan that looks fine on paper.
What this tool does
Alongside the deterministic projection, a Monte Carlo simulation runs hundreds of randomized return paths and reports the probability your money lasts — capturing sequence-of-returns risk that average-based tools miss entirely.
The problem
Most tools lump all savings into one bucket, ignoring that a dollar in a 401(k) is worth less than a dollar in a Roth or a taxable account after taxes.
What this tool does
Tax-deferred, Roth, and taxable accounts are tracked separately, with the right tax treatment on each — ordinary income on tax-deferred withdrawals, capital gains on taxable growth, and tax-free Roth. Withdrawals follow a tax-efficient order, and RMDs are forced once you reach the required age.
The problem
Inheritances are usually ignored, even though an expected inheritance can materially change how much you need to save.
What this tool does
Each person can enter an expected inheritance as an optional lump sum arriving at a chosen age — it flows into the plan at the right time.
The problem
The transition when one spouse dies is rarely modeled, even though it's a real financial cliff: the survivor files as single (higher rates) and one Social Security benefit stops.
What this tool does
The model handles the first death — switching to single filing, dropping to the larger survivor Social Security benefit, continuing pensions at their survivor percentage, and rolling the deceased's IRAs to the survivor.
Projections use recent federal tax brackets, standard deductions, and RMD tables as a baseline, inflated forward using your assumptions. State income tax rates come from current published rates. RMD start ages follow SECURE 2.0 rules based on birth year. The full details — including the withdrawal order and the Monte Carlo method — are on the methodology page.
Read the full methodology →This is a work in progress and I’d love to hear what’s useful, what’s missing, or what’s confusing. Reach out at bill@horyzen.com.
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