To do your financial projections well, you need to start the balance sheet and then adjust it according to assumptions in the cash flow. How you start your balance sheet depends on what numbers you have.
If you’re an existing or ongoing company, startup costs and startup funding are irrelevant. Use an estimated ending balance to set up the beginning balance of the planning period. I say estimated, in this case, because usually you’re doing your business plan to start a new period in a few months, such as working in October for a plan starting the following January. So you don’t actually have the ending balance for the year that’s going to end in December; but you do have pretty good numbers to estimate.
I usually recommend a past performance table showing three years of data, even though you actually use just that last year, which normally includes some estimates of ending balances and full-year data. Here’s an example.
If you’re planning a new company, just starting, then you set your starting balances using the estimated starting costs you did for basic business numbers. Your startup costs include assets and expenses. The expenses affect your capital, because they add up to a loss at startup (don’t be disappointed, that’s the way almost all startups begin. That loss means you’re keeping track of expenses so you can deduct them from taxable income later, when you make a profit).
You know that assets have to equal capital and liabilities. You’ve got assets defined in the startup table, so what’s left is to show where the capital and liabilities are. These are, between them, what you’ve used to pay for those expenses and assets. Here’s an example: