How sales work and why calculate interest
We come across promotions every day: in grocery supermarkets, clothing stores, when buying airline tickets or ordering goods on the Internet. Bright yellow and red price tags with the words “-20%”, “-50%” or “Black Friday” attract attention and promise great benefits.
Many buyers are accustomed to completely trust what is written on the window. However, the ability to independently calculate the final cost of a product is a basic financial literacy skill. It helps you plan your budget, check the honesty of sellers, and quickly assess whether the promotion is really profitable or just a marketing ploy.
What is one percent? (Mathematical base)
Before moving on to the formulas, let's remember the school curriculum. The word “percent” itself comes from the Latin expression pro centum, which literally translates as “per hundred” or “per hundred.”
For example, if sneakers cost 5,000 rubles, then 1% of their cost is 50 rubles (5,000 / 100 = 50). Knowing this simple rule, you can solve any problem involving markdown.
Two main formulas for calculating discounts
Depending on what exactly you need to know, you can use two different mathematical approaches. Choose the one that seems more convenient to you.
Method 1. How to find out the amount of savings in rubles
This method is suitable if you want to find out exactly how much money will remain in your wallet thanks to the promotion.
- Formula: (Starting price / 100) × Discount amount = Saving amount.
- Example from life: You buy a smartphone for 40,000 rubles. The store offers a 15% discount.
- We count: Divide 40,000 by 100 (we get 400). We multiply 400 by 15. We get 6000. Your net savings will be 6000 rubles! And the phone itself will cost 34,000 rubles (40,000 - 6000).
Method 2. How to immediately find out the final price at the checkout
This method is a little trickier, but it allows you to find out in one action the amount that will need to be paid to the seller.
- Logic: All goods are always 100%. If the store gives you 20%, then you only have to pay 80% of the cost (100 − 20 = 80).
- Formula: Starting price × 0.80 = Final price.
- Example: A jacket costs 8,000 rubles. The markdown is 30%. So you pay 70% (or 0.7 as a decimal).
- We calculate: 8000 × 0.7 = 5600 rubles payable.
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Secrets of mental calculation: how to do without a phone
In a store, it’s not always convenient to take out a smartphone, open an application and press buttons. There are some great math hacks that can help you figure out prices in your head in a couple of seconds.
| Discount size | How to quickly count in your head? | Example (from price 1200 rub.) |
|---|---|---|
| -10% | Simply remove the single zero at the end (or move the comma one place to the left). | Removing zero: saving 120 rub. |
| -20% | Find 10% (removing the zero) and simply multiply that result by two. | 120 × 2 = saving 240 rub. |
| -25% | This is exactly a quarter of the price. Just divide the initial cost by 4. | 1200 / 4 = saving 300 rub. |
| -50% | The simplest promotion. This is exactly half. Divide the original number by 2. | 1200 / 2 = saving 600 rub. |
Inverse problem: how to find out the percentage at two prices
Sometimes the old price (for example, 2500 rubles) and the new price (2000 rubles) are written on the price tag, but it is not indicated what percentage it is. To check the benefit you need:
- Find out the difference in rubles: 2500 − 2000 = 500 rubles markdown.
- Divide this difference by the old price: 500 / 2500 = 0.2.
- Multiply the result by 100: 0.2 × 100 = 20%.
For instant and error-free calculations of any, even the most complex amounts (for example, a 13.5% discount on 4890 rubles), you can always use our discount calculator.