TI Finance Programs and Javascript Equivalents

Thanks to Jim O'Connor, here are five handy finanial programs that will work for most any TI Calculator (TI-82, TI-83, TI-84, etc.). I have provided working Javascript equivalents here just in case you can't find your calculator. At the end of the page are worksheets and links to download these programs directly. You may wish to combine these into a single program with a menu, or make up your own programs to answer the worksheet questions. You may also wish to see the javascript code by viewing the source on your web browser or write a Excel spreadsheet that will make these calculations.

(If you are typing this program, press [PRGM] and select the [NEW] menu with the right arrow, then name it. In the editor, you can Find Disp and Prompt by pressing [PRGM]>[I/O] . You can find If, Lbl, and Goto by pressing [PRGM]>[Ctl]. The right Arrow is the [STO>] button on the bottom left. If you are typing text, the quote is [ALPHA][+], and you can go in and out of ALPHA-lock with [2nd][ALPHA]. If you cannot find a command, you can always find it alphabetically listed in the Catalog [2nd][0]-- typing the key with the first letter skips down to that that letter)

COMPINT

Stands for compounded interest. You simply put money in an account in one lump sum and it accrues interest over a period of time. The interest could be compounded monthly, yearly, quarterly, etc.

For example, if you invested $1,000 for 8 years in an account that pays 6.75% compounded monthly, you would have $1,713.41 at the end of those 8 years.

TI BASIC Javascript 
:Disp "AMOUNT INVESTED"
:Prompt A
:Disp "INTEREST RATE"
:Disp "IN PERCENT"
:Prompt I
:Disp "COMPOUNDED"
:Prompt N
:Disp "TIME IN YEARS"
:Prompt T
:A(1+(I/(100N)))^(NT)→Q
:round(Q,2)→Q
:Disp Q
Amount Invested:
Annual Interest Rate (in percent):
Compounded (times per year):
Time (in years):

Amount with the Compounded Interest:

MORTGAGE

Computes your monthly payment. You borrow money from a lender at a certain interest rate and you make monthly payments to the lender for the specified numbers of years.

For example, if you borrow $15,000 to be paid back in 5 years (60 monthly payments) with 8% interest, you monthly payment would be $304.15.

TI BASIC Javascript 
:Disp "LOAN"
:Prompt L
:Disp "INTEREST RATE"
:Disp "IN PERCENT"
:Prompt I
:Disp "TIME IN YEARS"
:Prompt T
:I/100→I
:(1+I/12)^(12T)→K
:(LIK)/(12(K-1))→M
:round(M,2)→M
:Disp "MONTHLY PAYMENT"
:Disp M
Loan:
Annual Interest Rate (in percent):
Time (in years):

Monthly Payment:

ANNUITY

Computes the amount when your annuity matures. An annuity is when a set amount of money is deposited into an account (usually monthly) and it grows with interest over the number of years invested. Retirement accounts are good examples of an annuity.

At age 21 you decide that instead of smoking you are going to put the money you would spend on cigarettes into an annuity. So you put $25 a month into an annuity that offers 7.43% interest until you retire at age 66. You would then have $109,804.84 in your account.

TI BASIC Javascript 
:Disp "MONTHLY PAYMENT"
:Prompt P
:Disp "INTEREST RATE"
:Disp "IN PERCENT"
:Prompt I
:Disp "TIME IN YEARS"
:Prompt T
:I/100→I
:1+I/12→K
:(PK(K^(12T)-1))/(I/12)→F
:round(F,2)→F
:Disp "FUTURE VALUE"
:Disp F
Monthly Payment:
Interest Rate (in percent):
Time (in years):

Annuity:

STILLOWE

It is the amount of money you still owe a lender after a period of time or series of monthly payments. The way it works is, the lender always takes the interest on the amount of money you owe from the monthly payment and what is left is deducted from the principle or the amount you still owe.

Example: The first month’s interest on the loan below is calculated by taking 1/12 of the interest rate on the amount you owe. which is an interest payment, the rest of your payment goes to principle (which isn’t much). Each following month’s calculation is the same. If you have $10,000 on a credit card that charges 18% interest, and made a monthly payment of $200 for 6 years (6*12=72 payments) you still owe $3,596.14 even though you paid $200*72 = $14,400. If you were paying $300 a month, you would have paid it off in under 4 years (46 payments+$164.74 on the last month).

TI BASIC Javascript 
:0→C
:Disp "LOAN"
:Prompt L
:Disp "INTEREST RATE"
:Disp "IN PERCENT"
:Prompt I
:I/100→I
:Disp "MONTHLY  PAY"
:Prompt M
:Disp "NO. OF PAYMENTS"
:Prompt N
:Lbl 1
:L(1+I/12)-M→L
:C+1→C
:If C<N
:Goto 1
:Disp "STILL OWE"
:round(L,2)→L
:Disp L
Loan:
Interest Rate (in percent):
Monthly Payment:
Number of Payments:

You still owe:

FUTVAL

Is the reverse of an annuity. If you know the amount of money you will need in the future (your retirement, kids college education, etc), you can calculate the approximate amount of money you will need to put into an account each month. You will have to consider inflation and a guess on the long term interest rates, but it will give you an idea of the amount you need to save. You are also neglecting any taxes on the interest.

Note: Use the ANNUITY program to calculate the amount of money you would have in savings after 30 years if the interest rate is 8% and you put $100 into the account every month. You should get $150029.52. Now check this with the FUTVAL program. The future value you want is $150029.52 at 8% for 30 years and you should get $100 as monthly payments.

TI BASIC Javascript 
:Disp "FUTURE VALUE"
:Prompt F
:Disp "INTEREST RATE"
:Disp "IN PERCENT"
:Prompt I
:Disp "TIME IN YEARS"
:Prompt T
:I/100→I
:1+I/12→K
:(I*F)/(12*K*(K^(12T)-1))→P
:round(P,2)→P
:Disp "MONTHLY PAYMENTS"
:Disp P
Future Value:
Annual Interest Rate (in percent):
Time (in years):

Monthly Payments (what you should save every month):

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