# Marginal Cost Calculator

URL: https://speedycalculator.com/calculators/finance/marginal-cost/
Last updated: 2026-10-25

> The marginal cost calculator works out the cost of producing one more unit – the change in total cost divided by the change in quantity – and compares it with price to show whether to expand production.

## Inputs

- Initial total cost
- Initial quantity
- New total cost
- New quantity
- Selling price per unit

## Results

- Marginal cost
- Change in total cost
- Change in quantity
- Decision

## Formula

```
Marginal cost = (new total cost − old total cost) ÷ (new quantity − old quantity)
```

## Explanation

Profit is maximised where marginal cost equals marginal revenue. In the short run marginal cost usually falls, then rises as capacity is stretched (diminishing returns).

### How to use the Marginal Cost Calculator

- **Initial total cost**
- **Initial quantity**
- **New total cost**
- **New quantity**
- **Selling price per unit**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter the total cost and quantity before and after the change, and the selling price.

### Tips

- Use consistent periods (a year or a quarter) for flow figures and period-end values for balances.
- Average opening and closing balances when a ratio mixes a flow with a stock.
- Benchmark against competitors in the same industry.
- Read the ratio together with others – profitability, liquidity and efficiency tell different stories.

### Common mistakes to avoid

- Using sales instead of cost of goods sold for inventory ratios.
- Mixing gross, operating and net profit.
- Ignoring one-off items that distort a single year.

### Inputs explained

FieldWhat to enterInitial total costAmount in your currencyInitial quantityA numberNew total costAmount in your currencyNew quantityA numberSelling price per unitAmount in your currency

### What each result means

- **Marginal cost** = ([New total cost] - [Initial total cost])÷([New quantity] - [Initial quantity])
- **Change in total cost** = [New total cost] - [Initial total cost]
- **Change in quantity** = [New quantity] - [Initial quantity]

### Example values

How the main result changes when **Initial total cost** changes and everything else stays at the example values above:

Initial total costMarginal cost25,00015537,50092.550,0003062,500-32.575,000-95100,000-220

## Worked example

Inputs — Initial total cost: $50,000; Initial quantity: 1,000; New total cost: $56,000; New quantity: 1,200; Selling price per unit: $35.

Results — **Marginal cost = $30.00**; Change in total cost = $6,000.00; Change in quantity = 200; Decision = Price exceeds marginal cost – extra units add profit.

## FAQ

**What is marginal cost?**
The extra cost of producing one more unit.

**Where is profit maximised?**
Where marginal cost equals marginal revenue.

**Why does marginal cost rise eventually?**
Diminishing returns as capacity fills up.

**What formula does the Marginal Cost Calculator use?**
Marginal cost = (new total cost − old total cost) ÷ (new quantity − old quantity).


## Sources

- [Corporate Finance Institute – financial ratios](https://corporatefinanceinstitute.com/)