Linda retired from a Defense agency at 62 and opened her TSP statement the week after her last day. $912,400. She read the number aloud to her husband across the kitchen table, and they both grinned. Nearly a million dollars.

Three months later she requested her first withdrawal of $5,000. The deposit that landed in her checking account was noticeably smaller. Her next question was a good one: whose money was that, exactly?

The number on the statement

If most of your savings sit in a traditional TSP or traditional IRA, the balance is a gross figure. Every dollar went in before tax, and every dollar comes out as ordinary income. Think of it as a joint account with a silent partner who has not yet told you their share.

That share is not fixed. It depends on your other income, your filing status, your state, and how you sequence withdrawals. A $912,400 balance might be worth $800,000 to you, or $700,000, depending on decisions you make in the first few years of retirement. Plan with the full balance and you risk overspending. Plan with the wrong haircut and you risk underspending a retirement you earned.

What a withdrawal really costs

The federal bracket

Take a married couple, both retired, with a $36,000 FERS pension and a $40,000 annual TSP withdrawal. That is $76,000 of income. With a standard deduction of roughly $30,000 (it changes yearly, so check irs.gov), taxable income lands near $46,000. The federal tax comes to about $5,000, an average rate under 7 percent on the whole $76,000.

That feels manageable. The trouble is that the average rate is not the number that matters when you decide how much extra to pull out. The marginal rate is, and it can jump in places people do not expect.

The Social Security overlap

Social Security benefits become taxable based on something called provisional income: your adjusted gross income, plus tax-exempt interest, plus half your benefit. For joint filers, the thresholds are $32,000 and $44,000. Those thresholds are set by statute and have never been indexed for inflation, so each year more retirees cross them.

Once you are between the thresholds, each extra dollar of TSP withdrawal can cause up to 85 cents of Social Security to become taxable as well. In the 12 percent bracket, that stacks up to an effective marginal rate of about 22.2 percent (12 percent times 1.85). Retirees sometimes call it the tax torpedo. It is not a separate tax, just the way two sets of rules overlap, and it hits hardest in the middle of the income range, not at the top.

Medicare, and your state

Two more items round out the drag.

Medicare Part B and Part D premiums rise with income through IRMAA surcharges, and the government looks at your tax return from two years earlier. A large withdrawal at 63 can raise premiums at 65. The thresholds change annually, so check the current table at medicare.gov or ssa.gov.

State tax varies wildly. Some states exempt retirement income entirely, some exempt federal pensions, and some tax everything. A couple moving from one to another can see the same $40,000 withdrawal cost them very different amounts. Look up your own state's rules before assuming anything.

Why withholding is not the answer

Back to Linda. Her smaller deposit came from federal withholding. For certain TSP payments paid directly to you, 20 percent is withheld automatically. That is a prepayment, not the actual tax. If her real tax rate on the withdrawal turns out to be 10 percent, she gets money back at filing time. If it is 24 percent, she owes more.

The practical point: do not treat what you receive as your tax answer. Withholding is a cash-flow tool. Run a rough projection of your full-year income, then adjust withholding to match. The TSP lets you set your own withholding on some payment types, and you can always make estimated payments to the IRS. Verify current options at tsp.gov.

Practical ways to shrink the drag

None of these are magic. Each one trades a bit of effort or a bit of tax now for a lower bill later.

Use the low-income years

Many federal retirees have a window between leaving work and starting Social Security (and before required minimum distributions begin) when their income is unusually low. Say you retire at 61 with a $50,000 pension and plan to claim Social Security at 67. Your taxable income might sit well below the top of the 12 percent bracket for joint filers, which has been near $100,000 in recent years. The room between where you are and that ceiling is cheap tax space. Filling it on purpose, often with Roth conversions, means paying 12 percent now instead of 22 percent or 24 percent later.

Convert gradually

A Roth conversion moves money from a traditional account to a Roth and makes the converted amount taxable that year. Converting a modest amount annually usually beats one giant conversion that vaults you into a higher bracket. Check tsp.gov to see whether in-plan Roth conversions are offered to you. Otherwise, a rollover to an IRA followed by a conversion is the usual path. Pay the tax from outside money if you can, because paying it from the converted funds shrinks the benefit.

Mix your buckets

If you have taxable savings, a traditional balance, and a Roth balance, you have a dial to turn. In a year when you want to stay below an IRMAA line or avoid the Social Security overlap, take more from Roth or taxable accounts and less from the traditional one. In a lean year, do the reverse. Flexibility is the real prize.

Watch the required minimum distribution clock

RMDs currently begin at 73 for most people and at 75 for those born in 1960 or later. A large traditional balance at that point forces taxable income whether you need it or not, and the pile can push you into higher brackets and surcharges. Shrinking the balance earlier is the main defense. If you are charitably inclined, qualified charitable distributions from an IRA (not the TSP) can satisfy part of the RMD without adding to taxable income.

A few honest caveats

Paying tax early is a bet. If your future rate turns out lower than you predicted, a conversion cost you more than waiting would have. If you move to a high-tax state, or tax law changes, your math changes with it. Nobody knows the brackets of 2040.

Also, early withdrawals before 59½ may carry a 10 percent additional tax, with exceptions such as separating from service in or after the year you turn 55. The rules differ between the TSP and IRAs, so confirm your situation before pulling money.

For a few hundred dollars, a session with a fee-only planner or a CPA who knows federal retirement can model your first ten years and often pays for itself. Bring last year's tax return and your latest statements.

Linda did that. She did not end up with a smaller retirement. She ended up with a clearer one, built around the roughly $780,000 she could count on, and a plan to convert a slice each year while her income stayed low. The silent partner never went away. She just stopped being surprised by them.