When to use this formula
Use this formula when your inputs match the variables and units shown below. It is most useful for checking a calculator result, recreating the calculation in a spreadsheet or understanding which input has the biggest effect.
Quick use
Use these formulas for quick business arithmetic, then verify tax, accounting and cash-flow treatment before making a formal decision.
Formula
Discounted price = original price x (1 - discount rate); markup price = cost x (1 + markup rate); margin = (revenue - cost) / revenue; break-even units = fixed costs / (unit price - unit variable cost); ROI = (gain - cost) / cost.
Variables
Use decimal rates in the formula, such as 0.20 for 20%. Revenue is money received before the cost being analyzed; cost should match the same product, campaign or time period.
Method notes
- Margin and markup are not the same: margin divides by selling price, while markup divides by cost.
- Break-even formulas assume a constant unit price and unit variable cost over the volume range.
- ROI works best with a clearly defined investment base and time period.
Example
If fixed costs are 12,000, unit price is 80 and unit variable cost is 50, contribution margin is 30 and break-even volume is 400 units.
Assumptions and limitations
These formulas do not replace accounting standards, tax rules or cash-flow modeling. They also exclude customer timing, refunds, credit losses, financing costs and inventory constraints unless the related calculator asks for them explicitly.
When the formula is not enough
- If the result depends on live prices, rates or official thresholds, check the latest value from the named source before relying on it.
- If the topic is medical, tax, legal, lending or safety related, use the result as a learning aid and check primary guidance before acting.
- If units or time periods differ, convert them before comparing results.
- If rounding affects the decision, keep extra precision until the final step.
Common mistakes
- Using markup when the decision needs margin.
- Mixing monthly fixed costs with annual unit volumes.
- Counting revenue but forgetting payment fees, returns or variable labor.
FAQ
Why look at the formula instead of only the answer?
The formula shows which inputs actually drive the result. That makes it easier to spot a wrong unit, compare two scenarios or explain the answer to someone else.
Can different calculators use different formulas for the same topic?
Yes. Some topics have multiple accepted methods or simplified variants. When that matters, the calculator should say which method it uses and what is excluded.
Are formula pages updated?
Stable math formulas need occasional review. Formulas that depend on changing rules, prices or thresholds need a dated source before the page can make stronger claims.