6 ways to calculate interest from the amount with the calculator and without - Lifehaker

1. How to calculate interest, dividing the number at 100

So you will find a numeric equivalent of 1%. Further it depends on your purpose. To calculate the percentages from the amount, multiply them by size 1%. To translate the number percentage, divide it to size 1%.

Example 1.

You go to the supermarket and see a share for coffee. Its normal price is 458 rubles, now there is a 7% discount. But you have a store map, and on it a package will cost 417 rubles.

To understand what option is more profitable, it is necessary to translate 7% in rubles.

Divide 458 per 100. For this, it is necessary to simply shift the comma separating the integer part of the number from the fractional one to the two positions to the left. 1% is 4.58 rubles.

Multiply 4.58 to 7, and you will receive 32.06 rubles.

Now it remains to take away from the usual price of 32.06 rubles. For action, coffee will cost 425.94 rubles. It means it is more profitable to buy it on the map.

Example 2.

You see that Steam is worth 1,000 rubles, although it used to be sold for 1,500 rubles. You are wondering how much percentage made a discount.

Divide 1,500 per 100. Matching a comma for two positions to the left, you will receive 15. This is 1% of the old price.

Now the new price divide 1%. 1 000/15 = 66.6666%.

100% - 66,6666% = 33,3333%. The store provided a store.

2. How to calculate interest, dividing a number by 10

This method is similar to the previous one, but it is much faster with it. But only if we are talking about percent, multiple five.

First you find the size of 10%, and then share or multiply it to get the right amount percent.


Suppose you put on a deposit of 530 thousand rubles for 12 months. The interest rate is 5%, capitalization is not provided. You want to know how much money will take a year.

First of all, it is necessary to calculate 10% of the amount. Divide it on 10, moving the comma to the left for one sign. You will receive 53 thousand.

To find out how much 5% is, divide the result by 2. This is 26.5 thousand.

If in the example it was about 30%, it would be necessary to multiply 53 by 3. To calculate 25%, it would have to multiply 53 to 2 and add 26.5.

In any case, such large numbers operate quite simple.

3. How to calculate interest, reaching the proportion

The proportions are one of the most useful skills to which you have taught at school. With it, you can count any interest. The proportion looks like:

The amount constituting 100%: 100% = part of the amount: a percentage proportion.

Or you can burn it like this: A: B = C: D.

Typically, the proportion is read as "but refers to b as well as refers to D". The work of extreme members of the proportion is equal to the product of its average members. To learn an unknown number of this equality, you need to solve the simplest equation.

Example 1.

For calculations, use the rapid browni recipe. You want to prepare it and bought a suitable chocolate tile weighing 90 g, but you could not have kept and bit off a piece of one. Now you have only 70 g chocolate, and you need to know how much oil is put instead of 200 g.

First, calculate the percentage of the remaining chocolate.

90 g: 100% = 70 g: X, where x is the mass of the remaining chocolate.

X = 70 × 100/90 = 77.7%.

Now we make a proportion to find out how much oil we need:

200 g: 100% = x: 77.7%, where x is the desired amount of oil.

X = 77.7 × 200/100 = 155.4.

Consequently, in the dough you need to put about 155 g of oil.

Example 2.

The proportion is suitable for calculating the profitability of discounts. For example, you see a blouse for 1,499 rubles at a discount of 13%.

First, find out how much the blouse is in percent. To do this, take 13 from 100 and get 87%.

Make a proportion: 1 499: 100 = x: 87.

X = 87 × 1 499/100.

Pay 1,304.13 rubles and wear a blouse with pleasure.

4. How to calculate interest with the help of relations

In some cases, it is possible to use simple fractions. For example, 10% is 1/10 of the number. And to find out how much it will be in numbers, it is enough to divide the whole for 10.

  • 20% - 1/5, that is, it is necessary to divide the number on 5;
  • 25% - 1/4;
  • 50% - 1/2;
  • 12.5% ​​- 1/8;
  • 75% is 3/4. So, you will have to divide the number 4 and multiply by 3.


You found pants for 2,400 rubles with a 25% discount, but you only have 2 000 rubles in your wallet. To find out whether there is enough money to new things, spend a series of simple computing:

100% - 25% = 75% - the cost of trousers as a percentage of the initial price after the application is applied.

2 400/4 × 3 = 1 800. It is so much rubles that pants are.

5. How to calculate interest using the calculator

If you are not a sweet life without a calculator, all calculations can be done with it. And you can come even easier.

  • To calculate the percentages from the amount, enter a number equal to 100%, the multiplication sign, then the desired percentage and the% sign. For an example with coffee computing will look like this: 458 × 7%.
  • To find out the amount less than percent, enter a number of 100%, minus, percentage size and a%: 458 - 7% sign.
  • Similarly, you can add as in the example with the deposit: 530,000 + 5%.

6. How to calculate interest with online services

Not all percentages can be calculated in the mind and even on the calculator. If we are talking about the profitability of the contribution, overpayments on mortgage or taxes, complex formulas are required. They are taken into account in some online services.


How to calculate interest from the amount: PlanetCalc

The site contains different calculators that calculate not only percentages. There are services for lenders, investors, entrepreneurs and all those who do not like to read in the mind.

PlanetCalc →.

Calculator - reference portal

How to calculate interest from the amount: Calculator - Reference Portal

Another service with calculators for every taste.

Calculator - reference portal →


How to calculate interest from the amount: AllCalc

Catalog of online calculators, 60 of which are designed to calculate finances. You can calculate taxes and penalties, the size of the subsidy on the housing and much more.

AllCalc →

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