Business tax season always makes me think about this scene from Schitt’s Creek. David thinks his company will pay for his new bedding (because he’s “thinking of bringing homeware into the store” he manages) and skincare (because he’s “the face of the company”). Why? “It’s a write-off.”

“Do you even know what a write-off is?” asks his bewildered father. “Yeah,” David insists. “It’s when you buy something for your business and the government pays you back for it.”

We’re supposed to laugh at David. But like many jokes, there’s some truth here. Lots of new business owners assume they can deduct “anything from my hairdresser all the way down to my gym shoes,” says tax professional Miklos Ringbauer, a CPA in southern California.

Ringbauer is the founder of MiklosCPA, a firm that advises business owners, and teaches federal taxation at Orange Coast College. I reached out to him for a reality check about writing off business expenses.

Here’s how it works: Say you sell muffins at your local farmers market and earn $500. You spend $50 on ingredients to make the muffins and $50 to rent your spot. If you write off those expenses, you’ll only pay taxes on the $400 you took home. That might shrink your tax bill by $20 or so — not by the full $100 you spent.

Ingredients are almost definitely a business expense in this scenario. The gym shoes you wear at the farmers market? Most likely not (even if you’re on your feet a lot). But what about the home office that doubles as your guest room? Or the car you drive for your daily errands, but also for deliveries?

Ringbauer walked me through best practices when you’re deciding what to deduct.

Draw a line between your business and personal finances as soon as you can. That will make it much easier to sync transactions with your accounting software and track what you spent where.

You also won’t have to dig through your personal credit card statements to figure out which Amazon purchase was your office chair and which was that humidifier for your bedroom.

What to do: Use a dedicated business bank account from the start, if you can. If your business has already launched, open a business account as soon as possible.

Here are our picks for the best business checking accounts. You can open most of these online in just a few minutes.

Lots of people travel for meetings and take clients to dinner. But if you’re audited, the IRS tends to scrutinize this kind of spending closely, Ringbauer says.

You can claim travel and entertainment as business expenses. Just be realistic about whether the event is “ordinary and necessary” for your operations. For example: A salesperson often needs to take executives out to dinner. But a doctor typically doesn’t need to wine and dine their patients.

What to do: Ringbauer tells his students: Look in the mirror and explain the deduction you’re taking. “If you buy (the explanation), then it’s most likely a deductible expense,” he says. “If you try to convince yourself in the mirror that it’s a business expense, most likely it’s not.

It might feel like all you ever do in your home anymore is work. But you can’t write off 100% of your rent or your mortgage as a business expense.

If your business is unincorporated or you’re a single-member LLC, you can deduct the cost of your home office as long as you use it exclusively for business and it’s your primary office.

What to do: Use a dedicated space for your home office. A separate ADU or garage is easiest, Ringbauer says, since it’s less likely you’ll use it for anything else. A specific bedroom isn’t bad. A desk in the corner is hardest.

Here’s our walkthrough of how much you can deduct for your home office.

If you claim a vehicle as a business expense, be prepared to prove that you mostly use it for your business.

All vehicles aren’t the same, and the IRS knows that. You probably don’t take the kids to the movies in the van you drive to HVAC jobs. But if you claim a BMW as a business expense and have no way to prove you use it for work, an auditor might have questions, Ringbauer says.

What to do: Keep mileage logs to track how much you use your vehicles while doing business. And again, be honest about whether a new SUV is necessary for your operations.

Audits don’t happen overnight. If the IRS does come knocking, it might not be for several years. That’s why it’s so important to take detailed records immediately — and keep them indefinitely.

“The biggest challenge most small-business owners face is, when they start, they just jump in,” Ringbauer says.

What to do: Start using accounting software, if you don’t already. You can set up your business bank account and credit card so they automatically export transactions to that software. Then, in most cases, you can upload your receipts so they’re saved alongside the transaction.

Here are NerdWallet’s picks for the best accounting software tools. Need some help tracking down receipts at the end of the month? Consider hiring a bookkeeper. (Here’s how much it tends to cost.)

NerdWallet’s Karrin Sehmbi finds and shares these grant opportunities.

The Amber Grant from WomensNet awards $10,000 to three small-business owners every month. At the end of the year, winners are automatically entered to win an additional $50,000 given to three lucky businesses.

The application is short and sweet. Just enter your contact info and business name. Then respond to two short-answer prompts asking about your business idea and how you would use the money if you receive the grant. You will also need to pay a $15 application fee.

WomensNet accepts applications on a rolling basis and will announce the next winners on Feb. 21.

Click here to see the application.

You’re eligible to apply if you’re a woman over 18 years of age, and your business is at least 50% women-owned. You must also operate within the U.S. or Canada.

Not a fit? Visit our small-business grants page for more than 50 more grant opportunities and tips for securing a grant.

President Donald Trump recently expressed support for capping credit card interest rates at 10%. Senator Bernie Sanders (D-Vt.) introduced a Senate bill proposing the same change a year ago. We don’t know if that change will happen. But it made me curious about how much interest small businesses pay on their credit cards.

The answer: $156 per month in credit card interest charges on average, according to last year’s annual small-business survey from Intuit QuickBooks. That'd be close to $1,900 a year. And Intuit found those totals are rising, up $50 per month from the previous year's report.

Credit cards are useful for bridging cash flow gaps, especially in your first few months when you can’t qualify for loans. But they’re expensive. Here are the best alternatives as your business matures: