LoanCalc

Loan Amortization tool built in Powershell. Uses the System.Windows.Forms classes built into C#.

Note: This script only supports Windows OS, even though it supports Powershell Core.

Getting Started

• Download from Github.
• Open a powershell session from the repo's directory.
• Right-click and select 'Run with Powershell' or run the below in a powershell session:

Powershell Core (7.0)

pwsh .\LoanCalc.ps1 

Legacy Powershell (5.1)

powershell .\LoanCalc.ps1 

This is a graphical diffrence when you run the app from Powershell core vs legacy powershell. See below for more.

GUI

Legacy Powershell

Powershell Core

Payment Schedule Generation

Data tables in Windows Forms have not been updated, thus there is no noticable diffrence between

Note: The schedule is only generated when Generate Schedule is toggled On. The schedule can also be generated on its own, without the need to run LoanCalc.ps1. See section on LoanCalc_sched.ps1 for more info.

Functionality

The app can perform the following calculations:

• Find Monthly Payment Amount
• Find Total Loan Amount
• Find Term of the Loan

Find Monthly Payment Amount

Monthly payment (A) can be found with the APR, Loan term (n), and Total Loan amount (P). APR is divided by 12 to provide the Monthly Interest rate (i).

        i * P  
A = ────────────── 
    1 - (1 + i)^-n 

In this example, the total loan amount is `$1000`, the APR is `1.0%`, and the loan term is 72 months.

Monthly Interest rate:
0.833 = 0.01 / 12


P = 1000                   0.000833 * 1000
i = 0.000833   ~14.32 = ──────────────────────
n = 72                  1 - (1 + 0.000833)^-72


The Monthly payment is `$14.32`.

Find Total Loan Amount

Total payment (P) can be found with the APR, Loan term (n), and Monthly Loan payment (A). APR is divided by 12 to provide the Monthly Interest rate (i).

        1 - (1 + i)^-n
P = A x ────────────── 
              i

In this example, the monthly loan payment is `$100`, the APR is `1.0%`, and the loan term is 72 months.

Monthly Interest rate:
0.833 = 0.01 / 12


A = 100                          1 - (1 + 0.000833)^-72
i = 0.000833   ~$6985.43 = 100 x ──────────────────────  
n = 72                                  0.000833


The total loan amount is `$6985.43`.

Find Term of the Loan

The term of the loan (n) can be found with the APR, Total Loan Amount (P), and Monthly Loan payment (A). APR is divided by 12 to provide the Monthly Interest rate (i).

            1 - (i * P) 
      log ( ─────────── )
                 A       
n = - ───────────────────
         log ( 1 + i )

In this example, the monthly loan payment is `$100`, the APR is `1.0%`, and the total loan amount is `$1000`.

Monthly Interest rate:
0.833 = 0.01 / 12

                             1 - (0.000833 * 1000)
                       log ( ───────────────────── )
A = 100                              100
i = 0.000833   ~11 = - ─────────────────────────────
P = 1000                   log ( 1 + 0.000833 )


The term of the loan is `11` Months.

Amortization Scheduling

This functionality can be achieved via two methods.

• via LoanCalc.ps1 (Toggle Generate Schedule = On in the GUI)
• via LoanCalc_sched.ps1

The schedule is generated based on inputs and desired calculation. This allows the schedule to forcast alternative payment plans. To achieve this, select the # of Payments option under Find:. Then ensure your desired payment is entered.

Note: By default, the schedule assumes one payment per month. This, and the intervals unit of Months can not be changed as of now.

LoanCalc_Sched.ps1

This is the core script to generate the schedule in a System.Windows.Form form. This script is triggered when Toggle Generate Schedule = On in the GUI. This section provides as example on how to run this script via command line.

.\LoanCalc_sched.ps1

# or

.\LoanCalc_sched.ps1 -TotalAmount 1000 -NumoPayments 72 -APR 0.01 -MonthlyPayment 100

Due to how the evaluation works, the schedule will ignore the Number of payments parameter -NumoPayments if the loan has been paid off early. In the example above, the schedule will end after the 11th payment; not continuing until the 72 month requirement was met.