(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)

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 |

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 |

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 |

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 |

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 |

- https://www.mathorama.com/ti/ - TI-8x Programs
- https://www.mathorama.com/casio/ - Casio fx-CG-50/9570/9850 programs
- Interest-Mortgage-Annuity Worksheet

- Interest Worksheet

- Zip file containing the TI Programs

(See education.ti.com for free connectivity software that sends programs to your calculator) - Pay It Off calculates total interest paid and how many monthly payments required to pay off a load with compounded interest.