Year-End Tax Moves That Save Thousands Before December 31

Step 1: Max Out Your 401(k) Before the December 31 Deadline

The 2025 401(k) contribution limit is $23,500 ($31,000 if you're 50 or older, thanks to catch-up contributions). Every dollar you contribute reduces your taxable income dollar-for-dollar. At a 24% marginal rate, maxing out a $23,500 contribution saves you $5,640 in federal taxes alone.

This is the single highest-leverage move for most earners. Unlike IRAs, 401(k) contributions must come from payroll deductions, which means you need to act now. If you're behind on contributions, log into your 401(k) portal and increase your deferral percentage immediately. Your December 31 paycheck may be the last chance.

Quick math: If you're currently contributing 6% on a $120,000 salary ($7,200/year) and bump it to 10% ($12,000/year) for the final two pay periods, you'll add roughly $1,600 in pre-tax contributions and save around $384 in federal taxes just from those two checks. Small adjustment, real money.

Step 2: Harvest Tax Losses in Your Taxable Brokerage Account

Tax-loss harvesting means selling investments at a loss to offset capital gains you've realized elsewhere in your portfolio. Long-term capital gains are taxed at 0%, 15%, or 20% depending on income. If you have $15,000 in realized gains and harvest $10,000 in losses before December 31, you only pay tax on $5,000 in net gains. At a 15% rate, that's $1,500 saved.

You can also use up to $3,000 of net capital losses to offset ordinary income each year. Any losses beyond that carry forward to future tax years, so they're never wasted.

Two critical rules to follow. First, the wash-sale rule: if you sell a security at a loss and buy the same or a "substantially identical" security within 30 days before or after the sale, the IRS disallows the loss. To preserve the deduction, hold off on repurchasing the same fund for 31 days, or immediately buy a similar-but-different fund (e.g., swap a Vanguard S&P 500 fund for a Fidelity S&P 500 fund). Second, settlement: stock trades typically settle in one business day (T+1) as of 2024, but you need the trade executed before December 31, not settled.

Log into your brokerage account today. Sort by unrealized gains and losses. The tax savings are sitting right there.

Step 3: Make Your Roth Conversion Before the Calendar Resets

A Roth conversion moves money from a traditional IRA or 401(k) into a Roth IRA. You pay income tax on the converted amount now, but all future growth is tax-free. The math works best when you're in a temporarily lower tax bracket, perhaps due to a job change, a business loss, or you're in a gap year before Social Security or RMDs begin.

The formula: convert up to the top of your current bracket. If you're a single filer with $60,000 in taxable income in 2025, you're in the 22% bracket (which runs to $103,350). You could convert up to $43,350 without crossing into the 24% bracket. On $43,350 converted at 22%, you'd owe roughly $9,537 in additional federal tax, but all future growth on that balance is tax-free forever.

You have until December 31 to do a Roth conversion for the current tax year. There's no extension. Use our Roth IRA calculator to model how much a conversion today compounds over 20 or 30 years. The long-term numbers often surprise people.

One honest caveat: Roth conversions increase your AGI, which can affect Medicare premiums (IRMAA), financial aid eligibility, and phase-outs for other deductions. Run the full picture before converting.

Step 4: Front-Load Charitable Giving with a DAF or Bunching Strategy

The standard deduction in 2025 is $15,000 for single filers and $30,000 for married filing jointly. If your itemized deductions (mortgage interest, state and local taxes capped at $10,000, charitable gifts) don't exceed the standard deduction, your charitable contributions save you exactly zero in taxes.

Two strategies change that.

Bunching: instead of giving $5,000/year for three years, give $15,000 in a single year. That one year you clear the standard deduction hurdle and capture real tax savings. The charities still get the same total over time.

Donor-Advised Fund (DAF): contribute a lump sum to a DAF before December 31 to claim the deduction this year, then recommend grants to your chosen charities on your own timeline (next year, the year after, whenever). The contribution is irrevocable, but the investment grows tax-free inside the fund. A $20,000 DAF contribution at the 24% bracket saves $4,800 in federal taxes this year, even if the underlying charities don't receive the grants until 2027.

If you own appreciated stock, contributing shares directly to a DAF is even more powerful. You avoid capital gains tax on the appreciation and deduct the full fair market value. A share bought at $10k and now worth $30k contributed to a DAF avoids $3,000 in long-term capital gains tax (at 15%) and generates a $30,000 deduction.

Step 5: Check Your FSA Balance and Use It Before It Expires

Flexible Spending Accounts (FSAs) are use-it-or-lose-it by default. The IRS allows employers to offer either a $640 rollover (the 2024 limit; check your plan for 2025) or a 2.5-month grace period extending to March 15. But many plans offer neither. If your FSA has a hard December 31 deadline, unused funds are forfeited.

The typical FSA contribution limit in 2025 is $3,300. If you have $1,200 sitting in an FSA you haven't used, that's $1,200 that disappears January 1 unless you act. Eligible expenses include prescription glasses, dental work, physical therapy, acupuncture, and hundreds of other medical items. Stock up on FSA-eligible over-the-counter products (pain relievers, first-aid supplies, contact lens solution) if you need to spend down a balance.

Check your plan documents or log into your FSA administrator's portal now. The deadline is real.

Step 6: Time Your Income and Deductions Strategically

If you expect your income to be lower next year (a planned sabbatical, a business with a slow Q1, nearing retirement), defer income into January where possible and accelerate deductions into December. If you expect your income to be higher next year, do the opposite.

For self-employed people and business owners, this is especially actionable. You can delay sending a December invoice until January 1, pushing that income into next year's return. You can prepay January's business expenses or rent in December to deduct them this year.

For W-2 employees, the levers are smaller but real. You can ask your employer to defer a year-end bonus into January if your company permits it. You can prepay your January mortgage payment before December 31 to capture one extra month of mortgage interest deduction (assuming you itemize).

The core principle: taxes are calculated on when income is received and when deductible expenses are paid, not when they're earned or incurred. Timing is the tool.

Worked Example: Sarah, 38, Single, $130,000 Salary

Sarah is a project manager with a $130,000 gross salary. Her marginal federal bracket is 24%. She has a taxable brokerage account, a 401(k) she's been under-contributing to, and $8,000 sitting in a traditional IRA she opened in a lower-income year.

Here's what she does before December 31:

401(k) top-up: Sarah has two pay periods left and increases her deferral to max out the remaining $4,000 she hasn't contributed this year. Federal tax saved: $4,000 x 24% = $960.

Tax-loss harvest: She finds $6,000 in unrealized losses in an international equity ETF and sells it. She had $4,000 in realized gains from selling company stock earlier in the year. Net gains drop to zero, saving her $600 in capital gains tax (15% rate). The remaining $2,000 of losses offsets ordinary income, saving another $480 (24% rate). Total saved: $1,080.

Roth conversion: Her taxable income after the 401(k) contribution is roughly $104,000 (after standard deduction of $15,000). She's near the top of the 22% bracket. She converts $5,000 from her traditional IRA to a Roth IRA at 22%, paying $1,100 in additional tax now. The $5,000 grows tax-free for 27 years. At 7% nominal growth, that $5,000 becomes approximately $32,000 at age 65, all tax-free.

DAF contribution: She donates $12,000 worth of appreciated stock she's held for three years (original cost $4,000, now $12,000) to a DAF. She avoids $1,200 in capital gains tax and deducts $12,000. Combined with her mortgage interest of $9,000 and SALT of $10,000, her itemized deductions total $31,000, clearing the $15,000 standard deduction and generating $16,000 in incremental deductions. At 24%, that's $3,840 in additional federal tax savings.

Total tax saved by December 31: roughly $5,880 in real 2025 dollars, plus a Roth account that compounds tax-free for three decades.

Want to see these numbers for your own situation? Build your free financial plan at Rightmont and we'll show you exactly which moves apply to you before the deadline.

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