If you already have a retirement plan built in another tool, you do not have to start from scratch here - but you do have to retype it. The work is much faster if you collect the numbers first and enter them second, rather than switching back and forth between two windows twenty times.

Budget half an hour for a plan of ordinary complexity. Most of that is gathering, not typing.

Collect these first

Listed in the order our pages ask for them, so you can work straight down the sheet once you start entering. Skip anything that does not apply.

Download the printable capture sheet (PDF) - room to write next to every field, with space for nine accounts, fourteen recurring expenses, and the rest. Easier than working from a screen while your other planner is open in the same window.

What to collect	Units and basis
Birth year, for you and your spouse	Year only - the plan works in whole years of age, so no month or day is needed
Retirement age, and the age to plan through	Ages, each person separately
State of residence	Drives state tax treatment of retirement income
Every account: balance, type, and owner	Write down what it actually is - 401k, Roth IRA, HSA, brokerage, savings - and pick the match from our list
Cost basis on taxable brokerage accounts	Dollars. Only taxable accounts need it.
Salary and any other income: start and end ages, any raise or growth rate, and whether it is self-employment	Monthly, gross, in today's dollars - before payroll tax, before contributions, before income tax
What you contribute to retirement accounts out of each paycheck, and any employer match	Which account it goes to, then either a percent of pay or a fixed amount. Match is a rate plus a cap - 50% of your contribution up to 6% of pay, say.
Social Security: the age you plan to claim, and the monthly benefit at that age	Monthly. See the warning below - this is the most commonly mis-entered number on the list.
Pensions: monthly amount, start age, payout option, and whether it has a COLA	Monthly, in today's dollars. Payout option means single life, or 50 / 75 / 100% joint and survivor.
Recurring expenses, by category	Monthly, in today's dollars
How much of each expense is essential	A percentage per row. Drives the funded ratio and any spending rule.
One-time expenses: amount and the year or age	Today's dollars
Windfalls: inheritance, property sale, settlement - amount and the age it arrives	Net - what actually lands in the account after tax, fees, and selling costs. Today's dollars, or flip the row to future dollars if you already know the nominal figure.
Debts: balance, rate, and required payment	Payment is monthly
Your other tool's return and inflation assumptions	Percentages. Note whether they are nominal or real.

Six things that are easy to get wrong

These are the ones that produce a plan that looks fine and is not. Worth reading before you start rather than after.

1. Every recurring dollar figure here is monthly, never annual. Expenses, salary and other income, pensions, Social Security, debt payments - all monthly. If your other tool shows annual figures anywhere, copying them straight across overstates by twelve times. This is the single most common mistake. On spending it is usually caught, because the plan fails so obviously; on income it is not, because a plan that suddenly looks great rarely gets questioned.
2. The Social Security amount is the benefit at the age you selected, not your full-retirement-age amount. We work backwards from the pair to figure out the rest, so the two fields have to agree with each other. If you pick age 70 and paste in your full-retirement-age figure, you understate the benefit by roughly a quarter for the whole plan. Your Social Security statement lists the amount at several ages - take the one matching the age you entered.
3. Enter everything in today's dollars. We inflate amounts forward for you. If your other tool displays a future-dollar value - what an expense will cost in 2041 - do not copy that figure in, or it gets inflated a second time. Windfalls are the one exception: each carries a today's / future toggle, so a known nominal amount can go in as-is.
4. Your plan starts now, not at retirement. It is tempting to model only the retirement years, but inflation indexing runs from the start of the plan, so a plan that begins at your retirement age puts every amount on a different footing than one that begins today. Enter your current age and current balances and let the plan run through the working years.
5. Do not forget what goes into the accounts while you are still working. Payroll contributions and the employer match are easy to leave out, because most tools show them somewhere other than the income screen. Leaving them out understates the balance you retire on, and the match especially - it is free money compounding for however many years you have left, and a plan without it can look meaningfully worse than the one you actually have. Enter the salary gross and let us take the contribution out, rather than entering take-home pay, or the deduction gets counted twice.
6. Account owner matters on a couple plan. Required minimum distributions key off each person's age, and what happens at the first death depends on whose account it is. On a single-person plan you can ignore this.

Then match the assumptions

If you are rebuilding a plan in order to compare the two, this step is the comparison. Two plans built on different assumptions will always produce different numbers, and that difference tells you nothing. Line these up before you read anything into the result:

• Inflation rate. The most consequential number in the file and the most likely to differ silently. Check it first.
• Expected returns, and whether the other tool quotes them before or after inflation.
• Asset allocation, including whether it shifts as you age.
• Turn any spending rule off, on both sides, before you compare. Guardrails, dynamic spending, adaptive withdrawals, Guyton-Klinger - the names differ but they all do the same thing, cutting spending when the portfolio falls, which raises the reported chance of success. If one plan has a rule running and the other does not, you are not comparing plans, you are comparing rules. Get the two unassisted baselines to agree first, then switch the rule back on to see what it is worth. Ours, Adaptive Spending, is off unless you turn it on; in other tools something similar is often on by default, which makes it easy to miss.
• What the success number counts. Ours means the money did not run out, and nothing else. See Monte Carlo simulations.

Setting your own return and inflation rates is a Plus feature. The free tier will build the whole plan, run the simulation, and tax it against your actual state, but it will not let you dial the assumptions to match another tool.

Once both plans assume the same things, whatever difference survives is real and worth investigating. That is the whole point of building the second one - see using this as a second opinion.