Withdrawal Sequence

Because the buckets are drawn in a fixed waterfall order: taxable first, then tax-deferred, then Roth. A larger taxable balance lets the taxable bucket cover more of the Annual Withdrawal Need on its own, leaving less unmet need to pass along to the tax-deferred bucket -- so the suggested tax-deferred draw falls (or holds flat once the remaining need reaches zero) as the taxable balance grows.

No. Roth is drawn last in this model's fixed sequence, so it has no way to influence what gets suggested for the taxable or tax-deferred buckets -- those two are fully determined by the taxable balance, the tax-deferred balance, and the Annual Withdrawal Need before Roth is considered at all.

Not necessarily. Each bucket is capped at 4% of its own balance, and if the sum of all three caps falls short of the Annual Withdrawal Need, the calculator surfaces that gap directly as Unmet Need (Shortfall) rather than leaving the three suggested amounts silently add up to less than what was requested.

It doesn't change any of the three suggested draw amounts at all -- those are determined purely by account balances and the withdrawal need. The tax bracket only feeds into the separate Approx Tax on Deferred figure, which estimates tax owed on the tax-deferred portion of the withdrawal after the sequencing is already decided.

The general reasoning behind this ordering is that Roth withdrawals are already tax-free, so there's no tax benefit to accelerating them, while leaving Roth balances invested longest maximizes the time they can compound without ever being taxed -- spending down taxable and tax-deferred money first is generally considered more tax-efficient over a long retirement.