"Oops."

It's only one word; just these 4 little letters nobody wants to hear. Especially those that run small businesses. With every penny on the line, this one word can make or break your bottom line.

According to a 2016 survey, 36% of small businesses stated that cash flow management was a challenge and 43% mentioned that growing revenue is tough.

What are the biggest money mistakes small business owners make and how can you avoid these potential pitfalls to keep your doors open for years to come? Here are the five most critical missteps to avoid.

1. Hitting the ground running without a foundational business plan

Your business plan is the foundation of your small business. It’s the blueprint you will use to structure your operations and measure your progress. When the time comes, your business plan is also what will help you convince others that working with or investing in your business is the right decision.

This is a huge misconception: Your business plan is not simply a fundraising tool. A solid business plan is a roadmap to help you lay out marketing and operational milestones.

“I’m not even making a profit. I don’t need a separate business account.”

2. Not separating your personal and business financial accounts

Wrong! From the second you earn money for your services, you’re a small business owner. Freelancer, consultant, entrepreneur, solopreneur: These are just titles that we use to distinguish our roles, but at the end of the day, when you’ve got income you’re declaring on a 1099, you need a separate bank account.

You don’t even have to set up a business account to begin with; a checking account that you will only use for transactions involving your business ventures will be enough in the beginning. You want to be able to keep track of every penny coming and going related to your business. When you do finally incorporate, and when tax time rolls around, you’ll have a clear ledger without your personal expenses complicating your business finances.

3. Not planning for tax liability

Ah, taxes. You may have bristled upon seeing the amount of taxes deducted from your paychecks when working a full-time job, but at least those were relatively simple. Once you branch out on your own and start receiving full payments from clients/customers, you’re now solely responsible for tax liability. If you’re starting a web-based small business, accounting can still feel simple, especially if you have an invoicing system set up for clients. But as your business grows, it’s easy to get caught up in the day-to-day management, neglecting tax responsibilities until April rolls around.

The easiest way to stay on top of your tax liability is to pay quarterly taxes on your income. You’ll also want to get familiar with state- and industry-specific taxes that’ll impact your small business.

Pro tip: Do things right from the start. Hire a professional to help you set up accounting processes for your business. Remember that business plan you started with? Those financial projections will also come in handy for planning for tax liability.

4. Being unprepared for a rainy day

Have you ever been caught in a rainstorm without an umbrella? Imagine that for your business — except the downpour impacts your inventory, your vendor payments and, worse, your customers. Most small business owners don’t even think about rainy day funds, especially when their business hasn’t begun to make a profit. But that’s precisely the reason it should be built into your budget from the start.

5. Not being proactive about taking on debt

You’ve scraped and saved, you’ve rolled up your sleeves, and you’ve built a business from the ground up. There’s a great deal of satisfaction to be found in pursuing your passion without going into debt.