Step-by-step tutorial

This tutorial introduces the quick calculator's function library and then shows the same project-oriented approach in a calculation sheet.

Quick-calculator loan example

Suppose we are calculating the monthly payment for a house loan. The existing balance is 300,000 and we need another 900,000, for a total of 1,200,000. The current monthly payment is 5,457, and the new budget allows 7,000 per month. The bank offers an annual interest rate of 3.45%.

Open the calculator, and chose “Finance” from the library popup. Press “AC” to clear out previous calculation if needed. On the upper popup, named “calculations around annuity loan”, press the popup and choose “years with fixed payment”. Then press “GO” to the right of the popup.

“YearAnnuityLoan(“ appears in the formula area, the bottom drawer opens with some explanation of the function.

The yellow message area ask for the first parameter:

Write 1200 000, and then press the “next” button.

The number show up in the formula area with a semicolon after as parameter delimiter.

In the yellow text field you have the next question.

Enter 12 months (write "12”) - press next:

Enter 7000 as the payment sum we would allow. Press next.

Enter 3.45 as the bank would give us (You are not supposed to press the % sign here). Press next. You now see that the formula is complete. The yellow bar is clear, and the function has got its closing parenthesis. The display show the result to be 19.7 years.

We now know that this loan we would take over at least 20 years, to fit in our budget. Let us calculate the exact payment. The extra expenses for the bank is 1900+1500, and they also take a transaction fee of 50 for each transaction. Lets calculate that.

Press the “AC” button to clear, Now chose the “Periodic payment value” in the popup and press GO.

The yellow bar:

Enter the loan sum, include the fees to the bank. Write 1200 000 + 1900 + 1500 press next.

Enter number of months, as 12*20, press next.

For this demonstration, enter the number of payments per year incorrectly as 12*20, then press next.

Press the interest rate, as 3.45 press next.

Ooops, this result does not seem to be correct. Lets look at the formula.

Here, we have included 12*20 on both number of months for the loan, and payments pr year.

Press the edit button to correct.

Change the last 12*20, to be only 12, press save.

Now, our result look better. We are close to what we calculated in the previous formula. We have changed 19.7 years to 20, and included the bank fees for establishment. To include the bank fee for the transaction, press “+50=” The formula area now show:

6998.355997 _? PaymentAnnuityLoan(1200000+1500+1900;12*20;12;3.45)+50=6998.355997

The first line after = has _? after the number, showing that the result is available to the next operator or function. If two people share the payment equally, divide it by two: enter /2=.

The formula area now show:

3499.177998 _? 6998.355997/2=3499.177998

Currently, we pay 5457 each month on the exisiting loan. To calculate how much more for each, we simply press "-5457/2=":

770.677998 _? 3499.177998- 5457/2=770.677998

If we had prepared an e-mail while we did those calculations, we would copy those values into the e-mail, while we where doing it, and also copy the text on the bottom drawer to document the parameters:

Calculation-sheet example

Open a calculation sheet and enter the assumptions as assignments. Descriptive camelCase names make the project easier to revisit:

$$\begin{aligned} \mathrm{existingBalance} &\colon\quad \text{existing loan balance} \\ \mathrm{additionalLoan} &\colon\quad \text{additional amount needed} \\ \mathrm{establishmentFees} &\colon\quad \text{one-time bank fees} \\ \mathrm{years} &\colon\quad \text{loan duration} \\ \mathrm{paymentsPerYear} &\colon\quad \text{payment frequency} \\ \mathrm{annualInterest} &\colon\quad \text{annual interest rate} \\[0.6em] \mathrm{existingBalance} &= 300000 \\ \mathrm{additionalLoan} &= 900000 \\ \mathrm{establishmentFees} &= 1500 + 1900 \\ \mathrm{years} &= 20 \\ \mathrm{paymentsPerYear} &= 12 \\ \mathrm{annualInterest} &= 3.45 \\ \mathrm{loanSum} &= \mathrm{existingBalance} + \mathrm{additionalLoan} + \mathrm{establishmentFees} \\ \mathrm{monthlyPayment} &= \operatorname{PaymentAnnuityLoan}\left(\mathrm{loanSum}, \mathrm{years}\cdot 12, \mathrm{paymentsPerYear}, \mathrm{annualInterest}\right) + 50 \\ \mathrm{sharedPayment} &= \frac{\mathrm{monthlyPayment}}{2} \end{aligned}$$

The calculated pane renders each expression and its result. You can adjust any assumption and run the sheet again, save the project as JSON, or create a titled PDF report.

This completes the tutorial.