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https://github.com/kenkundert/tvm

Time Value of Money
https://github.com/kenkundert/tvm

annuity financial interest loans money savings time-value-of-money

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Time Value of Money

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README 

        
TVM — Time Value of Money

=========================



.. image:: https://pepy.tech/badge/tvm/month

    :target: https://pepy.tech/project/tvm



.. image:: https://img.shields.io/pypi/v/tvm.svg

    :target: https://pypi.python.org/pypi/tvm



.. image:: https://img.shields.io/pypi/pyversions/tvm.svg

    :target: https://pypi.python.org/pypi/tvm/



:Author: Ken Kundert

:Version: 1.0.0

:Released: 2020-07-19



What?

-----



Time value of money calculations relate the following quantities:



- future value

- present value

- payments

- number of periods

- discount rate



*tvm* computes one of these values (other than discount rate) given the others.



The number of periods is split between two values, the number of years and the 

number of periods per year (the frequency).



Getting Started

---------------



Install using::



    pip3 install --user tvm



This installs *tvm* to ~/.local/bin; make sure this directory is on your path.



Usage::



    tvm [options] [fv|pv|pmt|years]



Options::



    -f , --fv      future value

    -p , --pv      present value

    -P , --pmt     payment per period

    -y , --years   total number of years

    -n , --freq    number of payments per year

    -r , --rate    annual discount rate

    -i, --ignore             ignore any previously specified values



If a value is not given it is recalled from the previous invocation.

Specify ``--ignore`` to use the default values for all unspecified options,

which are: *pv* = 0, *fv* = 0, *pmt* = 0, *years* = 30, *freq* = 12.



When the program runs, it always shows the specified values along with the 

computed value to make it easy for you to confirm that you used the right 

values.  The computed value is capitalized and shown in a different color to 

make it easier to pick out.



Savings Accounts

----------------



Consider case where you have a interest bearing account that pays 5% per annum 

compounded monthly. If you start with $10,000, you can compute the amount you 

will have after 5 years with::



    tvm --pv=10000 --rate=5 --freq=12 --years=5 fv



The amount in 5 years is referred to as the future value (fv). The current 

amount is the present value (pv). The frequency is the number of periods per 

year. The program responds with::



    pv = $10,000.00

    pmt = $0.00

    FV = $12,833.59

    r = 5%

    periods = 60

    years = 5



*periods* is the total number of periods and equals the product of the years and 

the number of periods per year.



You can specify values with SI scale factors, units, and commas.  The units and 

commas are ignored. So you can do the same thing with either::



    tvm --pv='$10,000' --rate=5% --freq=12 --years=5 fv



or::



    tvm --pv=10k --rate=5% --freq=12 --years=5 fv



The quotes are needed in the first case to prevent $ from being interpreted by 

the shell.



*tvm* remembers the values specified on the previous invocation and uses them if 

they are not specified.  This allows you to rapidly run what-if experiments 

without having to re-specify values that do not change.

So, once you have run the first command, you can now quickly determine how much 

you will have in 10 years using::



    tvm -y 10



    pv = $10,000.00

    pmt = $0.00

    FV = $16,470.09

    r = 5%

    periods = 120

    years = 10



Without changing anything else, you can determine what happens if you make an 

additional $100 contribution each month::



    tvm --pmt 100



    pv = $10,000.00

    pmt = $100.00

    FV = $31,998.32

    r = 5%

    periods = 120

    years = 10



Loans

-----



You can also use *tvm* to explore loans.  For example, you can compute the 

payment for a mortgage given the principal, interest rate, and length::



    tvm --ignore --pv=-250k --rate=4.375 --years=30 pmt



    pv = -$250,000.00

    PMT = $1,248.21

    fv = $0.00

    r = 4.375%

    periods = 360

    years = 30



The ``--ignore`` option was added so that we start from scratch; any values that

were previously specified are ignored.



You can now understand how paying a little extra affects how long it takes

to pay off the loan using::



    tvm --pmt=1.5k years



    pv = -$250,000.00

    pmt = $1,500.00

    fv = $0.00

    r = 4.375%

    periods = 257.08

    YEARS = 21.42



To compute the payments for a 5-year interest only balloon mortgage, use::



    tvm -y 5 -f -250k pmt



    pv = -$250,000.00

    PMT = $911.46

    fv = -$250,000.00

    r = 4.375%

    periods = 60

    years = 5