Libroffice PMT equivalent in python

[Michael Marshall]

On Thursday, April 25, 2013 6:46:01 AM UTC-4, ஆமாச்சு wrote:
> Hi,
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> 
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> Are there equivalent in any Python libraries that could match function
> 
> like PMT in libreoffice?
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> 
> 
> Refer: https://help.libreoffice.org/Calc/Financial_Functions_Part_Two#PMT
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> 
> --
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> 
> Amachu

The PMT function in spreadsheet programs (Excel, OpenOffice Calc, LibreOffice Calc, Symphony Calc, Gnumeric) and in pocket financial calculators (Texas Instruments BA II plus, HP 10B II, Casio Fc 100, 200) will provide an answer for the initial (periodic) payment. Whereas depending on the value of number of periods NPER there may be 5 different payments as explained below

0) the periodic payment
This is the payment that is in constant amount and is paid or collected over the life of investment assuming the number of periods are in whole and do not have a fractional part

If the number of periods have a fractional part such as 10.5 years of 119.25 months then besides the initial periodic payment, there may be 4 different last payments to choose from

1) Balloon payment
When the NPER has a fraction, then the last payment may be made or collected at the last full time period for example if NPER is 10.5 then the balloon payment is made at the end of year 10 where you pay the periodic payment plus the remaining principal and the interest due

2) Actual last payment
When the NPER has a fraction, you may opt to pay or collect the last payment at the actual time period. For example if NPER is 10.5 then you will make or collect the last payment at the end of 10 years and 6 months. This last payment will be the principal remaining after making 10 payments and will also include the interest on remaining principal

3) Drop payment
When the NPER has a fraction, you may opt to pay or collect the last payment at the end of the next full year. For example if NPER is 10.5 then you will make or collect the last payment at the end of 11 years. This last payment will be the principal remainining plus the interest on it

4) Partial period payment
But then if the NPER has a fraction, you may still opt to pay or collect the payment at the actual time period but the amount you pay is the fraction of time period times the remaining principal. Thus if the NPER is 10.5 you make the last payment at the end of 10 years and 6 months in amount of 0.5 * remaining_principal

Now the present value of the periodic payments plus the last payments from case 1, 2, 3 comes out to be the same as the loan amount. But this is not the case if we use payment from case number 4, in this instance the lender collects a few extra bucks from the borrower.

Excel financial functions were copied from those found in Lotus 123 and the financial functions in OpenOffice Calc, LibreOffice Calc, Symphony Calc are copies from Excel.

This Excel PMT function http://tadxl.com/excel_pmt_function.html offers the options of finding any of the 5 different payments as explained in the previous paragraphs. And it even goes further and finds all periodic payments when payments are growing, shrinking, increasing or decreasing. In this last case there may be as many different payments as there are number of periods. All this is part of tadXL add-in http://tadxl.com/