A practical guide to the one-income decision
Start with the real cost, not the salary
Most couples begin this conversation with the gross salary: one partner earns $95,000, so the question becomes "can we live without $95,000?" The more useful starting point is what that salary actually adds to the household each month. A second paycheck arrives after federal income tax, Social Security and Medicare, the 401(k) deferral and, in most states, state tax. Because it is stacked on top of the first salary, it is taxed at the household's highest rates, so its take-home share is noticeably lower than the first salary's.
Then set aside the costs that exist only because both of you work. Childcare is the largest for most families with a child under five. Commuting, parking, lunches, a work wardrobe and the convenience spending that happens when nobody has time to cook all shrink or disappear when one partner steps back. What remains is the real monthly cost of the change, and for many households it is much more manageable than the headline salary. The calculator above does that arithmetic for your numbers and shows the two figures side by side, which is usually the moment the decision starts to feel workable.
The tax and childcare arithmetic
Two effects make the real cost smaller than the salary, and both are mechanical rather than optimistic. The first is the tax wedge. The calculator estimates your household's federal income tax as a married couple filing jointly, using the standard deduction and the progressive brackets, plus employee payroll tax for each earner and a flat state rate you supply. It runs that estimate twice for every year, once with both salaries and once with the changed one, and the difference is the take-home that actually changes. Because the second salary sits in the higher brackets, that difference is smaller than the salary times your average tax rate.
The second effect is childcare. If the partner who steps back is the reason you no longer need full-time care, the saving is immediate and it comes from after-tax dollars. The calculator counts childcare as a cost both scenarios pay until your youngest starts kindergarten, then removes it from both. That timing is worth seeing clearly: a plan that is comfortable while childcare is being saved will have less room the year the saving ends, which is why the forecast shows every year rather than just the first.
The long-term costs, so they are in the plan
The monthly math leaves out two longer-term items that are easy to plan for once they are visible. The first is retirement. A 401(k) contribution and its employer match pause when the paycheck does. Over a three-year break at a modest salary that is tens of thousands of dollars that would otherwise have compounded for two or three decades. The full forecast grows those skipped contributions at an investment return you choose, to age 65, so you can see the order of magnitude. Some couples choose to redirect part of the childcare saving into the working partner's retirement account to offset it; treat the figure as a planning input, not a prediction of an account balance.
The second is re-entry pay. People who return after a multi-year break often come back a little below the pay they would have reached. The calculator defaults to a return at 85% of what the salary would have become, and lets you set it anywhere from zero to a raise. The alternative plan that returns at 70% is a useful check: if the household is fine either way, the plan does not depend on how the comeback goes.
Part-time versus stepping back fully
Part-time is its own option rather than a smaller version of stopping. On the income side, a part-time salary keeps some of the lowest-taxed dollars and often keeps the 401(k) match. On the cost side, it keeps a share of childcare, commuting and work costs, and it may or may not keep health coverage, since many employers set benefits at around thirty hours a week. Which comes out ahead depends on the specific numbers, which is why the calculator models both and the full forecast shows the one you did not pick as an alternative plan.
There is also a longer-term case for part-time that the spreadsheet cannot capture: staying attached to a field tends to make re-entry smoother. If the two options are close on monthly cost, that is a reasonable tiebreaker.
Questions worth settling together
What is the real monthly cost, and can we see it in our actual accounts? The number above is an estimate built from figures you typed in. Checking it against what actually leaves your accounts each month, including the irregular costs that estimates miss, turns an estimate into a plan.
What is the plan for when childcare ends anyway? If the saving that makes the plan work ends in three years, decide now whether that is also the return date, or whether spending will come down, or whether the remaining income will have grown enough by then.
Who provides the health coverage? If it comes from the job that is changing, price the replacement early. It is a single line that can be the difference between Tight and Comfortable, and it is easy to get a real quote for.
How much room do we want in the tightest year? Look at the year with the smallest margin in the forecast and picture a 10% dip in the remaining income. If you would pause saving for a year, that is a Tight plan, and it is a reasonable plan as long as you are both choosing it with open eyes.