Almost every dollar of tax you can still save is decided before December 31.

The safe harbour is the single most useful rule nobody explains

You do not have to predict your income accurately to avoid an underpayment penalty. You have to hit a safe harbour. Pay in at least 100% of what your total tax was last year — 110% if your adjusted gross income last year was over $150,000 — and the penalty does not apply, no matter how much more you end up earning this year.

That single fact removes most of the anxiety from estimated taxes. It converts an unknowable forecasting problem into a known number you can divide by four. For anyone whose income is genuinely unpredictable, the prior-year safe harbour is almost always the right target, with the balance settled at filing.

There is a second lever worth knowing about: tax withheld from wages is treated as paid evenly across the year regardless of when it was actually withheld. That means a withholding increase in November can retroactively cure an underpayment from March. If you or your spouse has a W-2, that is frequently the cheapest fix available.

What a projection actually looks at

We build the year from where it stands, then model what changing something does to it. In practice the moves worth the most tend to be the unglamorous ones:

Retirement plan choice. For a profitable one-person business the difference between a SEP-IRA and a solo 401(k) is often several thousand dollars of deductible contribution room at the same income, because of how the employee deferral works. The plan has to exist before the deadline, which is why this is an autumn conversation.

Timing. Income you can pull into this year or push into next, expenses you can accelerate, a fixed asset purchase that is worth more as a deduction in a high-income year than a low one.

The qualified business income deduction. It has thresholds and phase-outs that create sharp edges. Moving income across one of those edges changes the deduction disproportionately, and the interaction with wages paid is not intuitive.

Capital gains and losses. Harvesting losses, understanding which bracket long-term gains land in, and not tripping the wash sale rule on the way through.

Advice you can act on, and the line we will not cross

Tax planning is our work and we take it seriously. What we do not do is give legal advice, recommend investments or securities, or sell you a financial product — we are not attorneys, not investment advisers, and we do not earn commission on anything. Nothing we recommend pays us more than anything else we might recommend.

Where a plan needs an operating agreement drafted, a trust created, or an investment allocation chosen, we will say so and work alongside the attorney or adviser you choose. Our full scope of practice is here.