The last few weeks of the year are the best time to get ahead of tax season instead of scrambling in March. A few things worth doing before December 31:
Reconcile your books. Make sure every invoice, receipt, and expense for the year is actually logged, not just remembered. Use the annual business report to see your full-year numbers in one place.
Chase down unpaid invoices. Outstanding invoices from this year are worth a final push before year-end, check the aging report to see what's overdue and by how much.
Make your Q4 estimated tax payment. The final quarterly estimated tax deadline is typically mid-January, use the tax estimate tool to check you're not underpaying.
Consider retirement contributions. SEP IRA and Solo 401(k) contributions can often be made up until your tax filing deadline (with some rules around the following year), but knowing your numbers now avoids a rushed decision. See the SEP IRA and Solo 401(k) calculators.
Update your contracts and rates. If you're planning a rate increase for the new year, draft the rate increase letter now so it's ready to send to clients with advance notice.