When the plan needs cash, which balance it taps changes lifetime tax more than most return assumptions. The engine draws in a defined order, and you can change it.
The default order
Taxable → tax-deferred → Roth. Spend the least tax-advantaged dollars first and let Roth compound tax-free longest. One standing exception: a forced RMD always comes out of tax-deferred first. The IRS doesn't care about your preferred order.
Nothing else rearranges the order behind your back. If you want conversion-year spending funded from Roth, so living expenses don't consume the bracket headroom you're converting into, set that order yourself for the phase covering those years, under Money flow → Withdrawals.
What you control
- The draw order itself, per position in the sequence. One-time expenses (a down payment, a mortgage payoff, an extra principal payment) carry their own order, so a big single draw can come from a different pocket than daily spending.
- HSA balances, when present, sit outside the main order: qualified medical costs draw from HSA tax-free (displacing spending), and non-medical HSA draws after 65 are ordinary income.
- When in the year a one-time expense leaves. The projection runs a year at a time, so without a month a lump leaves on 1 January and gives up the whole year's growth on that money, about 3% of a large purchase dated October. Pick the month and the lump is drawn then, from what each account in the draw order has grown to by that month; the tax and the cut-back rule's set-aside treat it as the same lump either way, because the tax year is whole. The Housing panel's purchase has the same month field for its down payment.
Several one-time rows in the same year are drawn in calendar order, not in the order you typed them, and each is funded on its own. That matters twice. An earlier row takes its money before a later one has grown into it, so a January purchase leaves less behind for a July cost than the other way round. The answer no longer depends on which row you happened to enter first, or on the Housing panel adding its purchase after everything else. And each row settles before the next one starts: what a row cannot fund is reported as that row's shortfall, instead of being quietly covered later by a row you allowed into an account the first one was not. A restricted order still falls back to the usual accounts when the ones you named run dry, so naming an order changes where a row looks first, not the accounts it may ever reach.
Housing's own rows share the same position, in one fixed order. A manual one-time row you typed comes first, then a down payment, then any extra principal payments in the order they're listed, then an early payoff, all dated the same month settling in exactly that sequence, so a July manual withdrawal always leaves before a July down payment. Extra principal and payoff draws are uncapped: "Keep income under" (Money flow → Withdrawals) never limits a mortgage paydown, the way it never limits any other one-time expense; the panel shows the tax and Medicare/ACA consequence of that draw, but it does not promise the ceiling held.
A row dated a month that has already passed this year is still counted, drawn now, and so is a home purchase dated that way. The plan never assumes a lump was paid just because its month went by: an October purchase that slipped to November would otherwise vanish the day the month rolled over, and the success rate would jump with no change to your balances. The panel marks such a row "month has passed", and the Housing panel says so beside the month. Once the money has actually left, delete the row, because your balances already reflect it and counting it again would be counting it twice; for a home you have bought, switch Housing to Already own. If it has not happened yet, move its month.
"Withdrawal" here is the funding mechanic: which pocket the dollars leave. Your spending level is set in the plan; see spending vs. withdrawal for why the app keeps the two words apart.