Shopify deposits your payouts with zero tax withheld. That is the whole reason quarterly taxes exist for store owners: the IRS wants its cut as you earn, not in one lump the following April. If your store is a sole proprietorship or a single-member LLC, the profit flows onto your personal return through Schedule C, and you are responsible for prepaying the tax on it yourself.
The $1,000 rule for Shopify profit
The trigger is simple: if you expect to owe $1,000 or more in total tax for the year after any withholding from a day job, you are supposed to make estimated payments. Two taxes stack up on store profit. First, ordinary income tax at your personal rate. Second, self-employment tax at 15.3%, which covers Social Security and Medicare and applies once your net self-employment earnings reach just $400 for the year. A store clearing $2,000 a month in profit is well past both lines.
Your estimate is based on net profit, not on gross payouts. Revenue minus cost of goods sold, ad spend, apps, shipping, and fees is the number the tax applies to. A store doing $300,000 in sales at a 15% net margin owes tax on roughly $45,000, not $300,000.
Four payment dates that ignore your payout schedule
Estimated payments go in on Form 1040-ES, either mailed with a voucher or paid online through IRS Direct Pay or EFTPS. The due dates are April 15, June 15, September 15, and January 15 of the following year. Notice they are not evenly spaced: the second payment covers only two months of income. Sellers with a heavy Q4, which is most of ecommerce, often owe the largest chunk with the January 15 payment after the holiday season lands.
Miss a payment and the IRS charges an underpayment penalty that works like interest on the shortfall. It is not catastrophic, but it is pure waste, and it compounds the "surprise April bill" problem rather than solving it.
Safe harbor when your store is scaling
You do not need to predict your year perfectly. The safe harbor rule protects you from penalties if your four payments total at least 100% of last year's tax liability, or 110% if your adjusted gross income was over $150,000. For a store that is growing fast, paying to the safe harbor number is often the cleanest move: you avoid penalties even if this year's profit doubles, and you settle the true balance when you file.
A practical rhythm for a Shopify owner: close your books monthly, set aside 25% to 30% of net profit in a separate account, and drain that account into the IRS on each due date. States with income tax expect their own estimated payments on the same cadence, so check your state's voucher as well.