Stock Profit Calculator

Why I Built This Stock Profit Calculator

I've been trading stocks for years, and one thing that always frustrated me was trying to quickly calculate my actual profit or loss on a trade. Sure, my brokerage account shows it, but sometimes I want to run the numbers myself—before I even place a trade.

This calculator is designed for real-world trading. It doesn't just subtract buy price from sell price. It accounts for trading commissions, which can eat into your profits—especially on smaller trades. When you're trading 50 shares at $10 each, a $5 commission on each side matters. That's $10 in fees on a $500 investment—2% right off the top.

I use this calculator constantly when I'm:

• Planning a trade: "If I buy at $50 and sell at $55, how much will I actually make after fees?"
• Evaluating past performance: "I thought I made $500 on that trade, but what was my real return percentage?"
• Setting break-even targets: "What price do I need to hit just to cover my costs?"
• Comparing brokers: "How much will higher commissions cost me over time?"

How to Calculate Stock Profit: The Complete Formula

The math behind stock profits is straightforward, but you need to be careful not to miss any costs. Here's the exact formula I use:

Notice that the sell commission is subtracted from revenue, not added to cost. Mathematically it works out the same, but this is how I think about it: I receive money from selling shares, but the broker takes their cut before it hits my account.

Here's a real example: Let's say I bought 100 shares of XYZ at $50, with a $5 commission. Later, I sold them at $75, with another $5 commission.

• Total Cost: ($50 × 100) + $5 = $5,005
• Total Revenue: ($75 × 100) − $5 = $7,495
• Profit: $7,495 − $5,005 = $2,490

Understanding Profit/Loss Percentage

Dollar amounts are nice, but percentage return is what really matters. A $500 profit means something very different if you invested $5,000 versus $50,000.

In our example above: ($2,490 / $5,005) × 100 = 49.75%

That's a fantastic return! But here's why percentage matters: if I had only made $500 profit on that same $5,005 investment, my return would be just 9.99%. Same dollar amount as a completely different trade might be great or terrible depending on how much capital I used.

I generally look for:

• Under 10%: Disappointing, unless I held for a very short period
• 10-25%: Solid return, I'm happy with this
• 25-50%: Excellent trade, this is what I aim for
• Over 50%: Home run! Time to consider taking profits

The Impact of Trading Fees and Commissions

I can't stress this enough: commissions matter. In the days of $0 commission trades at most brokers, it's easy to forget that fees still exist. But not everyone has access to zero-commission trading, and even when you do, there are hidden costs.

Here's what I've learned about fees:

• Small trades get crushed by fees: If I buy 10 shares at $10 with a $5 commission, that's 5% in fees immediately. The stock needs to rise 10% just for me to break even (5% to cover buy commission, 5% to cover sell commission).
• Per-share fees add up fast: Some brokers charge "per share" fees for active traders or penny stocks. 1,000 shares at $0.01 per share = $10 each way. That's $20 in fees on a single trade.
• Option assignments/exercises have fees: If you trade options and get assigned, you might pay unexpected fees on the resulting stock transaction.
• SEC and FINRA fees: These tiny fees on stock sales are automatically deducted. You might not notice them, but they exist (usually a few cents per trade).

My calculator includes commission inputs because realistic profit calculation means accounting for every cost. When I'm evaluating a potential trade, I always assume the worst-case fee scenario to be safe.

Break-Even Price: What You Need to Know

The break-even price is the price at which I can sell my shares and walk away with neither a profit nor a loss. It's higher than my buy price because it needs to cover both buy and sell commissions.

In our example: $50 + ($5 / 100) + ($5 / 100) = $50.10

That means if I sell at exactly $50.10 per share, I make zero profit. I need to sell above that price to make money. On the flip side, if I'm worried about a stock dropping, I know I have some cushion—I can sell at $49.50 and still "only" lose 1%, not the 2% I'd lose if I ignored commissions.

I use break-even analysis to:

• Set stop-loss levels: If my break-even is $50.10, I might set a stop at $48 (about a 4% loss) to limit downside.
• Calculate profit targets: If I want a 20% return and my break-even is $50.10, I need to sell at $60.12.
• Evaluate trade quality: If the break-even is way above my buy price due to high fees, I might skip the trade entirely.

My Rules for Using This Calculator

After years of trading, I've developed some rules around tracking my profits:

• Always calculate before trading: I plug in the numbers before I buy. If the potential return doesn't justify the risk, I skip it.
• Be conservative with fees: If I'm not sure what the commission will be, I overestimate. Better to be pleasantly surprised than disappointed.
• Track annual returns, not just individual trades: A 50% gain on one trade doesn't mean much if I lost 40% on another. I calculate my overall portfolio return yearly.
• Consider holding period: A 20% return in 6 months is amazing. A 20% return over 5 years is mediocre (about 3.7% annualized).
• Don't forget taxes: Short-term gains (held under 1 year) are taxed at my regular income rate. Long-term gains (held over 1 year) get the lower capital gains rate. This calculator shows pre-tax returns—I factor in taxes separately.
• Compare to benchmarks: Did I beat the S&P 500? If the market returned 15% and I made 12% after fees, I actually underperformed.

Common Mistakes Traders Make

I've made plenty of mistakes over the years. Here are the most common ones I see traders make when calculating profits:

• Ignoring commissions: Thinking you made $500 when you actually made $490 after fees. Small trades get hit hardest.
• Forgetting about dividends: If a stock paid dividends while you owned it, that's part of your return. Add it to your profit calculation.
• Confusing paper gains with real gains: Your portfolio might show +$10,000, but you haven't actually made anything until you sell. (And once you sell, you'll owe taxes.)
• Not annualizing returns: A 10% return sounds good until you realize you held the stock for 3 years—that's only about 3.2% annualized, barely beating a savings account.
• Only looking at winners: We love to brag about our 50% gains but conveniently forget about the 30% loss. Calculate your aggregate return across all trades.
• Chasing high returns without considering risk: A 100% return is worthless if I had to take massive risk to get it. Consistent 15-20% returns with manageable risk beats a roller coaster any day.

When to Take Your Profits

One question I get all the time is: "When should I sell?" There's no perfect answer, but here's my framework:

• When the thesis is broken: I bought for a reason. If that reason is no longer valid (bad earnings, management change, industry shift), I sell regardless of profit or loss.
• When I hit my target: Before buying, I set a profit target. If I reach it, I take at least some profits off the table. Greed has cost me more than fear ever has.
• When the money is better elsewhere: If I'm up 30% but find another opportunity with a better risk-reward profile, I might sell to free up capital.
• When tax considerations matter: If I'm close to the one-year mark for long-term capital gains treatment, I might wait a few weeks before selling to save on taxes.
• When I need the money: Life happens. Sometimes I sell because I need cash for something else. It's not ideal, but it's reality.

The key is to have rules in advance. I decide when I'll sell before I buy. This removes emotion from the equation and keeps me from making impulsive decisions.