September 15 Is Closer Than You Think: 5 Tax Planning Strategies Every California Small Business Should Do This Week

Scheduled publication: 9:00 AM Pacific Time.

September 15 is more than another date on your business calendar. It is a tax planning checkpoint that can affect your cash flow, estimated payments, entity filings, owner tax liability, and year-end decisions.

For many businesses, September 15, 2026 is the deadline for the third federal estimated tax payment. It is also the extended federal filing deadline for calendar-year S corporations and partnerships that requested a timely extension. California S corporations may also have an extended Form 100S filing deadline on this date, while California partnerships and LLCs taxed as partnerships generally have a later October 15 extended filing deadline.

Waiting until December can be a missed opportunity. By then, several planning decisions may be more difficult to implement, and your business may have fewer options to manage taxable income and preserve cash.

This guide explains five tax planning strategies for small business owners to complete this week using the DEAL method and the SMART recording process.

Part 1: Build the Foundation Before September 15

I. Understand the September 15 Tax Deadline

Before taking action, define the obligations that may apply to you.

Estimated tax payment means a periodic payment toward the income tax you expect to owe for the year. Business owners commonly make these payments through their individual returns, while corporations may make payments at the entity level.

According to the IRS third-quarter tax calendar, September 15, 2026, includes:

• The third federal estimated tax installment for individuals.
• The third federal estimated tax installment for corporations.
• The extended filing deadline for calendar-year Form 1120-S returns when a timely six-month extension was requested.
• The extended filing deadline for calendar-year Form 1065 partnership returns when a timely six-month extension was requested.

The IRS also explains that estimated payments can result in an underpayment penalty if you do not pay enough by each deadline, even if you are due a refund when filing your annual return. Review the IRS estimated tax guidance for the general payment schedule.

Important distinction: An extension to file does not automatically extend the time to pay tax. A business can file an extended return on time and still face penalties or interest if required payments were not made.

California rules require separate review. The California Franchise Tax Board business due-date guidance should be used to confirm your entity-specific obligations. For example:

• A California S corporation may have an extended Form 100S deadline of September 15.
• California partnerships and LLCs taxed as partnerships generally have an extended filing deadline of October 15.
• California individual estimated tax installments follow a 30/40/0/30 schedule in many cases, meaning the September installment may be 0% of the annual required payment. However, the date remains an important planning checkpoint.

II. Strategy One: Apply the DEAL Tax Review Framework

The DEAL method gives you a practical way to organize your September tax planning.

Note: This DEAL framework (Document, Estimate, Act, Lock in) is the tax-planning version of TLC's methodology. It is distinct from the DEAL memory tool used in our accounting education content, where debits increase Expenses, Assets, and Losses.

D — Document your current numbers

Gather financial information through at least July or August:

• Year-to-date revenue.
• Operating expenses.
• Payroll and owner compensation.
• Accounts receivable and accounts payable.
• Business asset purchases.
• Prior estimated tax payments.
• Federal and California withholding.

E — Estimate your full-year results

Use current results to project:

• Full-year revenue.
• Net profit.
• Owner pass-through income.
• Taxable wages and distributions.
• Expected federal and California tax liability.
• Cash available for taxes and operations.

A — Act on the highest-priority items

Complete or schedule the actions that have a deadline:

• Calculate and submit the September estimated payment.
• Finalize extended S-corporation or partnership returns.
• Review Schedule K-1 information for owners.
• Confirm payroll tax deposits and filings.
• Evaluate available credits, deductions, and depreciation options.

L — Lock in monitoring

Do not end your review when the payment is submitted. Establish:

• A fourth-quarter estimate.
• A monthly bookkeeping review.
• A tax document checklist.
• A cash reserve target.
• A date for year-end tax planning before December.

The DEAL method prevents September planning from becoming a single transaction. It turns the deadline into a repeatable process for improving financial stability.

III. Strategy Two: Clean Up Your Records Using the SMART Recording Process

Accurate tax planning depends on accurate records. If your bookkeeping is incomplete, your estimate may be based on assumptions rather than business performance.

Use the SMART recording process:

• S , Sort: Organize transactions by bank account, credit card, payroll, loan, and payment platform.
• M , Match: Match deposits and expenses to invoices, receipts, contracts, and other source documents.
• A , Assign: Assign each transaction to the correct income or expense category.
• R , Reconcile: Reconcile bank and credit card accounts to identify missing or duplicated transactions.
• T , Track: Review trends in revenue, margins, cash flow, and expenses each month.

This process is especially important if your business uses both cash-basis and accrual-basis reporting. As explained in TLC’s cash-basis versus accrual accounting guide, the two methods recognize income and expenses at different points in time.

Your immediate goal is not to make your records look perfect. It is to create a reliable financial picture that supports a defensible estimate.

Part 2: Turn the Deadline Into a Year-Round Strategy

IV. Strategy Three: Recalculate Estimated Taxes and Coordinate Owner Payments

A September estimate should reflect what your business is actually earning, not what you expected six months ago.

Compare your projected full-year tax liability with:

• Prior-year tax liability.
• Q1 and Q2 estimated payments.
• Federal and California withholding.
• Current-year profit growth.
• Pass-through income from an S corporation or partnership.

For many individual taxpayers, a common safe-harbor approach involves paying at least 90% of current-year tax or 100% of prior-year tax, with a potential 110% prior-year threshold for certain higher-income taxpayers. The correct calculation depends on your facts, income level, filing status, and tax structure.

S-corporation and partnership owners should also coordinate entity reporting with personal estimates. A late or inaccurate Schedule K-1 can make owner-level planning more difficult. If the final return is not complete by September 15, use reliable year-to-date information and a conservative projection rather than postponing the review entirely.

V. Strategy Four: Review California-Specific Planning Opportunities

California business owners should not assume that federal and state planning produce the same result.

Review the following items with your tax professional:

• California estimated tax payments: Corporate and individual payment schedules may differ.
• S-corporation filings: Confirm whether your California Form 100S is due on September 15.
• Partnership and LLC filings: Confirm the applicable California extended deadline, which is generally October 15 for calendar-year entities.
• Pass-through entity tax: Verify whether your business elected California’s PTE tax, whether the required prepayment was made, and how the election affects owner-level estimates.
• California minimum franchise tax and LLC fees: Include these obligations in your cash-flow forecast.
• Payroll and reasonable compensation: S-corporation owners should review whether compensation remains reasonable and properly documented.
• Depreciation and business assets: Model the effect of Section 179, bonus depreciation, or other applicable elections before purchasing assets solely for a perceived tax benefit.
• Business credits: Investigate whether federal or California research, hiring, energy, or industry-specific credits may apply.

Tax deductions should support a sound business decision. Spending money only to reduce taxable income can weaken liquidity if the purchase is not necessary.

VI. Strategy Five: Create a Q4 Plan Instead of Waiting Until December

December is not the beginning of tax planning. It is often the point when several planning opportunities are already limited.

Before the end of September, create a written Q4 plan that includes:

• Expected fourth-quarter revenue.
• Planned hiring or compensation changes.
• Equipment and technology purchases.
• Retirement plan contributions.
• Outstanding receivables to collect.
• Vendor obligations and cash needs.
• Potential changes in entity structure or ownership.
• Final estimated tax targets.

Use your financial statements to compare actual performance against your budget. TLC’s guide to small business financial performance explains how income statements, balance sheets, cash-flow information, and key performance indicators can support better decisions.

The objective is flexibility. If revenue declines, you can preserve cash and adjust estimates. If revenue increases, you can prepare for the additional tax liability before it becomes a surprise.

Video resource: How to Create a Financial Plan for a Small Business

VII. Why Year-Round Tax Consulting Matters

A once-a-year tax return reports what already happened. Year-round tax consulting helps you make better decisions while there is still time to influence results.

TLC Business Solutions supports small and mid-sized businesses with:

• Tax planning and compliance.
• Bookkeeping and transaction management.
• Financial statement preparation.
• Payroll and filing support.
• Cash-flow forecasting.
• Business management consulting.
• Retirement and wealth-preservation planning.

Our flat-rate billing model is designed to make professional financial support more predictable. Instead of waiting for a large, unexpected bill during tax season, you can maintain an ongoing relationship with a financial team throughout the year.

With more than 30 years of industry experience, TLC's team has helped business owners identify errors, recover lost assets, improve reporting, and build practical financial systems. Past results are not a guarantee of future outcomes, but they reflect the depth of experience we bring to every engagement.

FAQ: September 15 Tax Planning

1. Is September 15, 2026, the deadline for every California business?

No. The deadline depends on your entity type, tax year, filing status, and whether an extension was filed. Federal calendar-year S-corporation and partnership returns on extension are generally due September 15. California partnership and LLC returns may have an October 15 extended deadline.

2. Does filing an extension delay my tax payment?

Generally, no. An extension usually provides additional time to file the return, not additional time to pay the tax owed.

3. Do California individual taxpayers owe an estimated payment on September 15?

California uses a 30/40/0/30 estimated-tax schedule in many situations, so the required September installment may be 0%. However, you should confirm your specific obligation and use the date to review your full-year tax position.

4. What records should I provide to my accountant?

Provide reconciled bank and credit card statements, payroll records, profit-and-loss reports, balance sheets, fixed-asset information, loan statements, prior payments, and documentation for significant expenses or business purchases.

5. Can tax planning still help after September 15?

Yes. The September deadline is a checkpoint, not the end of planning. Fourth-quarter projections, retirement contributions, compensation reviews, asset purchases, and year-end accounting adjustments may still require action.

Conclusion: Use September 15 to Improve Financial Stability

September 15 is an opportunity to replace last-minute tax preparation with a structured plan.

By applying the DEAL method, documenting reliable year-to-date numbers, using the SMART recording process, recalculating estimated taxes, reviewing California requirements, and creating a Q4 plan, you can make more informed decisions about cash flow and taxable income.

The key principle is simple: tax planning is most effective before the year is over. Waiting until December may mean fewer choices, less flexibility, and more financial uncertainty.

If you need support with small business accounting in California, estimated tax planning, or year-round financial management, visit TLC Business Solutions to learn how a predictable flat-rate model can support your business throughout the year.

External Resources

• IRS Third-Quarter Tax Calendar
• IRS Estimated Tax Payment FAQ
• California Franchise Tax Board Business Due Dates
• California Estimated Tax Payments
• California 2026 Form 100-ES Instructions
• IRS Publication 505: Tax Withholding and Estimated Tax

Disclaimer: This article is provided for general informational purposes only and does not constitute tax, accounting, legal, or financial advice. Tax rules, deadlines, elections, and safe-harbor requirements may vary based on your entity type, income, accounting method, filing history, and individual circumstances. Consult a qualified tax professional and confirm current requirements with the IRS and California Franchise Tax Board before making payment or filing decisions.