How to Log Side Income for Tax Time: Deposits, 1099s, and Quarterly Planning

What the IRS expects you to track

IRS materials on gig economy and self-employment income explain that net profit from a trade or business is generally taxable. Platforms may issue Form 1099-NEC when payments meet reporting thresholds (commonly $600 in a calendar year for many payers, per IRS instructions for information returns). You still owe tax on income even if no form arrives. Keep records of all payments and allowable business expenses.

A simple monthly log (spreadsheet or app)

• Date, payer/platform, gross amount, fees withheld by platform.
• Expense category: supplies, software, mileage (if you use a vehicle for business), home office share if applicable.
• Hours for net-hourly planning (Sidequity) separate from tax categories.
• Running net profit column: gross minus expenses.
• Reserve column: percent you set aside for federal, state, and self-employment tax planning.

Quarterly payments vs year-end shock

IRS Form 1040-ES instructions describe estimated tax for income not subject to withholding. Many calendar-year taxpayers make federal estimated payments in April, June, September, and January. Dates shift for weekends and holidays. Your W-2 withholding may cover part of your total tax; side profit can still trigger a balance due. Read estimated quarterly taxes for side hustlers for the calendar; this guide focuses on the log that feeds the number.

Mileage and receipts

• IRS publishes an optional standard mileage rate for business use (72.5 cents per mile for 2026 in IRS Notice 2026-10). Actual expense method is an alternative.
• Keep contemporaneous mileage logs for gig and client driving (see gig worker mileage and IRS rates).
• Save digital receipts for software, fees, and supplies; match to payout month.

What to give your preparer

• Annual income summary by payer (including amounts without 1099s).
• Expense totals by category with receipts for major items.
• 1099-NEC and 1099-K forms received.
• Mileage log or actual vehicle expense worksheet.
• Prior-year return if side income is new to you.

Sidequity takeaway

Logging side income is worth the hour each month if it prevents spending tax money. Pair the log with side-hustle-tax-reserve or after-tax-side-income for planning percents, then read w2 job and side hustle taxes together when you have both income types.

Suggested next steps

• Open a separate checking account for side deposits only.
• Reconcile last month’s platforms to bank deposits once.
• Set a recurring reserve transfer on payout days.
• Read understanding 1099-NEC side income when forms arrive.