# How to calculate compound interest?

#### Jakest

##### New Member
Also i just want to add something else you said which either i misunderstood or James missed.

For your newest example did you want to add 10% interest AND an extra \$10 each week?

sorry it is not my first language
i meant 10\$ and 10% raise each week
aka 1st week 10\$
2nd week 11\$
etc

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#### James006

##### Well-known Member
shouldn't be 10 instead of 1,000?
1'000 is the Initial Amount ...

10% is the WEEKLY interest rate

52 is the Number of Weeks ...

I proposed the mathematical formula ... to give you an opportunity to understand the underlying logic ...

If you only need to use Excel built-in functions ... as shown by Ahoync ... with FV ... you are getting the same results ...

#### James006

##### Well-known Member
sorry it is not my first language
i meant 10\$ and 10% raise each week
aka 1st week 10\$
2nd week 11\$
etc
If you mean 10 ... when you type 1'000 ...

Just replace 1'000 by 10 in the formula ...

Last edited:

#### Jakest

##### New Member
1'000 is the Initial Amount ...

10% is the WEEKLY interest rate

52 is the Number of Weeks ...

I proposed the mathematical formula ... to give you an opportunity to understand the underlying logic ...

If you only need to use Excel built-in functions ... as shown by Ahoync ... with FV ... you are getting the same results ...

something is wrong
i tried this 10 * ( 1 + 10% ) ^ 4 and returns 14\$ for 4 weeks
that cant be the case cos we have 10\$ every week without the 10% interest

#### Jakest

##### New Member
If you mean 10 ... when you type 1'000 ...
.

nah it is a different example

#### James006

##### Well-known Member
With your latest explanation ... there is NO compound interest ...

What there is ... it is a 10% increase of your weekly amount ...

With your initial amount in cell A1 : 10
With your inflation weekly rate in cell B1 : 10%
With your number of weeks in cell C1 : 52

You can test following formula in cell D1 :
Code:
``=C1*A1+(C1-1)*((1+(C1-1))/2)*(A1*B1)``
Hope this will help

#### James006

##### Well-known Member
Once you have tested the formula .... feel free to post your feedback