DrFaustCalc User Guide

A financial calculator that works the same way as the Texas Instruments (TI) financial calculator BA II Plus Professional. Every answer in this guide was checked on the calculator. Tap ↑ Contents at the bottom right to come back here from anywhere.

Contents

What does this label mean? → the search box above or the Glossary · How do I do this? → How-to examples

1. Getting started ↑ Contents

Six rules ↑ Contents

1. Number first, then the key. Type 360, then press N to store 360 in N.
2. To solve, press CPT and the unknown. Example: CPT PMT computes the payment. CPT is short for Compute.
3. In a worksheet (a group of input items for one function, more), store values with ENTER. Not =. Then press ↓ for the next item.
4. Money out is negative, money in is positive. Enter negatives with +/−. The − key subtracts. (Sign rule)
5. Clear before a new problem. TVM: in the standard calculator, 2ND FV (CLR TVM). Worksheets: 2ND CE|C (CLR WORK) inside the worksheet. Values survive power off. CLR TVM does not clear settings such as P/Y and BGN.
6. Orange labels above keys need 2ND first. Example: 2ND 7 → DATA.

Your first calculation ↑ Contents

Check the settings first ↑ Contents

Every example in this guide starts from the default settings below. The settings line shows P/Y · C/Y · END/BGN · DEC · angle · Chn/AOS. A setting that is not the default is orange. Check the date format in the SET tab. To restore all of them at once, use Defaults in the SET tab.

Settings inside worksheets (ACT/360 in BOND and DATE, 2/Y · 1/Y in BOND, the DEPR method, the STAT regression method) are not reset by Defaults. The examples that use them say how to check them.

Reading the display ↑ Contents

How a calculation flows ↑ Contents

2. Concepts — things that prevent mistakes ↑ Contents

This chapter is not about which keys to press. It explains why you press them. You can read the sections in any order.

Time value of money (TVM) ↑ Contents

100 today and 100 in one year are not worth the same. You can earn interest on 100 you get today. Time value of money (TVM) is the calculation of this difference.

The calculator links five values in one formula: N (number of periods) · I/Y (interest rate) · PV (value now) · PMT (money paid or received each period) · FV (value later). Enter four and it solves for the fifth. Enter 0 for a value you do not use.

This formula is right only when the periods are the same length, each payment is the same amount, and the interest rate does not change. If the amount is different each year, do not use TVM. Enter the amounts in CF (cash flow) and use NPV · IRR.

Sign rule — money in is +, money out is − ↑ Contents

In one problem, measure everything from one person. Money coming in to that person is + (positive). Money going out is − (negative). A negative answer means you must pay that amount.

For the borrower: the loan received, PV = +, and the payments, PMT = −. For the lender it is the opposite. When you solve for an amount (PV, PMT or FV), the sign of the answer tells you which way that money must go.

When you solve for the interest rate (I/Y) or IRR, the money must flow both ways. If all amounts are + or all are −, there is no answer and you get Error 5. A deal where you only pay and never receive has no rate of return. When you solve for the number of periods (N), you may get Error 5, or instead a meaningless answer such as a negative number. When you solve for an amount, you always get an answer.

Worksheets and item types ↑ Contents

A worksheet is a group of input items for one function. Press its key to open it. You see one item at a time and move with ↑ ↓.

TVM is a worksheet you use straight from the standard calculator. You do not move between items: type a number and press a key like N, and it is stored. Worksheet values stay after you leave. Before a new problem, clear them inside the worksheet with 2ND CE|C (CLR WORK).

END and BGN ↑ Contents

If each payment (PMT) is made at the end of a period, it is END (End). If it is made at the start of a period, it is BGN (Begin).

Ask: is the first payment right now, or one period from now? A loan is usually repaid starting one month later, so END. Rent that you pay when you sign the contract is BGN. The default is END.

BGN affects PMT only. If PMT is 0 (one lump sum), END and BGN give the same answer. BGN stays on until you switch it off — check for an orange BGN on the settings line. How to change it: P/Y · BGN

P/Y · C/Y — and why this guide keeps both at 1 ↑ Contents

P/Y (Payments per Year) is how many payments you make in a year. C/Y (Compounding periods per Year) is how many times interest is added in a year.

I/Y is really an annual rate. The calculator uses P/Y and C/Y to turn I/Y into the rate for one period. This guide keeps P/Y = C/Y = 1 and enters N and I/Y per period directly. 30 years monthly → N = 360; 4.5% a year → I/Y = 4.5 ÷ 12. The settings do not change, so you can see exactly what you entered.

C/Y must also be 1. Changing P/Y also changes C/Y. CLR TVM does not clear these settings. (ICONV has its own C/Y, so it does not affect TVM.) Example: the same loan gives −1,520.06 with C/Y 1 and −1,521.44 with C/Y 12.

Set P/Y and C/Y only when the payments per year and the compounding per year are different (e.g. a loan paid monthly with interest added quarterly). 8% a year, compounded quarterly, 30 years monthly, 300,000: 2ND I/Y 12 ENTER ↓ 4 ENTER 2ND CPT 360 N 8 I/Y 300000 PV 0 FV CPT PMT → PMT= −2,190.27. Here, enter the annual rate as it is (8) in I/Y. When you are done, press 2ND I/Y 2ND CE|C 2ND CPT to set them back to 1.

Nominal and effective rates ↑ Contents

A nominal rate is the rate for one compounding period times the number of periods in a year, with no interest on interest. An effective rate is how much money actually grows in one year.

A nominal 12% a year, compounded at 1% each month (interest also earns interest), really grows (1.01)¹² − 1 = 12.68% in a year. The more often interest is added, the higher the effective rate. If the problem already says "effective 12% a year", you do not need to convert. To convert, use ICONV.

Calculation order: Chn and AOS ↑ Contents

Chn (Chain) calculates in the order you press the keys. AOS (Algebraic Operating System) uses math order (nCr · nPr → powers → multiply and divide → add and subtract).

2 + 3 × 4 = → Chn gives 20 (2+3=5, 5×4). AOS gives 14 (3×4 first). The default is Chn, the same as the physical calculator. Exam preset in the SET tab switches to AOS.

In either mode, put the part to do first in parentheses and you get the same answer: 2 + (3 × 4) = 14, (2 + 3) × 4 = 20. Putting the whole expression in one pair of parentheses does not help. How to change it: All settings

Displayed and stored values ↑ Contents

The display only shows the value rounded to DEC decimals (default 2). Calculations use all the stored digits.

Example: if you enter 4.5 ÷ 12 in I/Y, the display shows 0.38 but the stored value is 0.375. Press and hold the result to see the unrounded value.

Two exceptions. ① AMORT and DEPR round to DEC decimals while they calculate, like the physical calculator. If you change DEC, the results change. ② ROUND (2ND STO) really rounds only the value on the display now. A PV or memory you already stored does not change. To use the rounded value, store it again. If DEC is F (9), ROUND changes nothing.

3. Key reference ↑ Contents

Top to bottom, as on the keypad. Grey text is the full English name. The right column is what the key does after 2ND.

Control keys (rows 1–2) ↑ Contents

TVM keys (row 3, green outline) ↑ Contents

TVM = Time Value of Money (concept)

Math keys (rows 4–5) ↑ Contents

Number keys and 2ND worksheets ↑ Contents

+/− changes the sign. Press it after typing the number.

Memory and clearing ↑ Contents

Computer keyboard (shortcuts) ↑ Contents

In this guide, press / to jump to the search box.

4. How-to examples ↑ Contents

Starting state: every example starts from the default settings (P/Y = C/Y = 1, END, DEC 2, Chn, US). Examples that change a setting show how to change it back. These examples keep P/Y = C/Y = 1 and set N and I/Y per period (why). 30 years monthly → N = 360; 4.5% a year → I/Y = 4.5 ÷ 12. You can type 4.5 ÷ 12 = I/Y directly.

What is my monthly loan payment? ↑ Contents

How much will I receive each month on money I lent? ↑ Contents

How much will a lump sum or monthly savings grow to? ↑ Contents

Present value of yearly payments (end or beginning of year) ↑ Contents

Remaining balance and how much interest did I pay ↑ Contents

Is this investment worth it? (NPV · IRR) ↑ Contents

Interest plus principal (bond-like cash flows) ↑ Contents

What should I pay for this bond? ↑ Contents

Depreciating a building or equipment ↑ Contents

How two values relate (regression) ↑ Contents

By how much did it grow? Annual growth rate ↑ Contents

Nominal rate to effective rate ↑ Contents

Days between dates · date after N days ↑ Contents

Cost, price and breakeven ↑ Contents

Working with Excel ↑ Contents

5. Worksheet reference ↑ Contents

Every function (worksheet) uses the same order: what it does → when to use it → what you need first → open · clear · leave → items → cautions → examples. For item types (Input · Compute · Auto · Setting) see Worksheets and item types. To leave any worksheet, press 2ND CPT (QUIT).

TVM — Time value of money ↑ Contents

For problems like loans, savings and annuities, where the same amount moves at the same interval. It solves for one of: number of periods, interest rate, amount now, amount each period, amount later.

• When monthly payment, savings at maturity, present value of an annuity, how many years it takes, what the interest rate is
• First check that P/Y = C/Y = 1 and END
• Open not needed (use it from standard mode) · Clear 2ND FV (CLR TVM) — only the 5 values go to 0; settings stay

Enter four and solve for one. Enter 0 for a value you do not use. When you solve for the interest rate and all amounts have the same sign, you get Error 5 (sign rule).

Examples: first calculation · loan · savings · annuity

P/Y · BGN — Payments per year and payment timing ↑ Contents

Settings that decide how TVM splits I/Y (P/Y · C/Y), and whether PMT is paid at the start or the end of each period (BGN · END).

• When with this guide's method (P/Y = C/Y = 1) you rarely change them. Use BGN when the first payment is right now, as with rent or a lease
• Clear on that screen, 2ND CE|C → P/Y and C/Y go to 1, BGN goes to END

Concepts: P/Y · C/Y · END and BGN

AMORT — Amortization (2ND PV) ↑ Contents

While you repay a loan, it shows the principal and interest paid over a range of payments, and the balance left after that range.

• When total interest paid in the first year, loan left after 5 years, balance before an early repayment
• First enter the loan's N · I/Y · PV in TVM and compute the payment with CPT PMT
• Clear 2ND CE|C → only P1 and P2 go to 1 (TVM values stay)

For a single payment, set P1 = P2. Like the physical calculator, it rounds to DEC decimals at each payment (displayed and stored values).

Example: remaining balance and interest paid

CF — Cash flow entry (CF) ↑ Contents

Where you enter, in order, cash flows whose amounts differ from year to year (period to period). NPV and IRR use these cash flows.

• When evaluating an investment, uneven income, bond-like flows of interest and principal
• Clear 2ND CE|C → deletes all cash flows (old values stay in the LOG)

All flows must be the same distance apart (e.g. 1 year). If they are one month apart, NPV's I, IRR and the payback periods are all monthly too. Example: 5,000 for 4 years in a row is one group: C03 = 5,000, F03 = 4. So if F01 = 12, C02 starts at period 13. Insert a row 2ND ↓ (INS) · delete a row 2ND ↑ (DEL). For a group of 0 cash flows, leave Cnn at 0.00 and press ↓ to Fnn to enter only the count.

Examples: NPV · IRR · bond-like cash flows

NPV — Net present value (NPV) ↑ Contents

All cash flows in CF, converted to today's value and added. If it is above 0, the investment earns more than the required return (I).

• When whether to invest, which of two investments is better, how many periods to get the money back
• First enter the cash flows in CF · Clear 2ND CE|C → I and the results (NPV · NFV · PB · DPB)

Example: is this investment worth it?

IRR — Internal rate of return (IRR) ↑ Contents

The interest rate that makes the NPV of the CF cash flows 0. In other words, the return per period the investment itself earns. If one CF period is a year, it is a yearly return; if it is a month, a monthly return.

• When comparing an investment's return with your required return. If money goes out first and after that only comes in (the sign changes once), the investment is worth doing when IRR is higher than the required return. If the sign changes several times, this comparison can be wrong, so decide with NPV
• First enter the cash flows in CF. To see MOD, also enter the financing rate (the rate you pay to borrow the investment money) as I in NPV · Clear 2ND CE|C → RI and the results (IRR · MOD)

Error 5 if the cash flows never change sign; Error 7 if they change sign several times and no answer is found.

BOND — Bonds (2ND 9) ↑ Contents

Converts a bond's price and yield into each other, and shows accrued interest and duration. Prices are per 100 of face value (face value = the original amount repaid at maturity).

• When what to pay for the yield you want, what yield you get at this price
• Clear 2ND CE|C → all items and the ACT · 2/Y settings go back to the start

Enter one of YLD and PRI and press CPT on the other. With the US setting, dates are MM.DDYY (6.1206 = 2006-06-12).

Example: what should I pay for this bond?

DEPR — Depreciation (2ND 4) ↑ Contents

When you spread the cost of an asset (a building, equipment) over the years you use it, this gives the depreciation for each year and the book value left. Book value = the purchase cost minus the depreciation so far.

• When this year's depreciation expense, book value after some years, comparing methods
• Clear 2ND CE|C → LIF and YR go to 1, CST and SAL go to 0. The method · starting month (M01) · DB rate · DT1 stay — for a new problem, enter these items again too

Change the method on the first item with 2ND ENTER. SL, SYD and DB match the formulas in the TI guidebook (CST and SAL are also rounded to the displayed decimals). The TI guidebook has no formula for DBX, SLF and DBF, so results may differ slightly from the real calculator. Example: depreciation

DATA — Statistics data (2ND 7) ↑ Contents

Where you enter numbers (one variable) or pairs of numbers (two variables) for statistics. See the results in STAT.

• Clear 2ND CE|C → deletes all data (old values stay in the LOG)

Insert and delete work as in CF. Example: regression

STAT — Statistics results (2ND 8) ↑ Contents

Shows the mean, standard deviation and regression line of the DATA values, and predicts values with the regression line.

• When the average and how spread out the data is, how closely two values move together, what y is when x is 10
• First enter data in DATA · Clear 2ND CE|C → method goes back to LIN, X' and Y' go to 0

In Ln · EXP · PWR, the means, standard deviations and sums use the log-transformed values (Ln: x, EXP: y, PWR: both). For the mean of the original data, switch to LIN. 1-V uses Y as counts, so it does not fit x · y pairs. If all X values are the same or there is only one data point, no regression line can be drawn, so only a · b · r (and, with one data point, the sample standard deviations Sx · Sy) show Error 1. Clear it with CE|C and move to another item with ↑ ↓.

Change the method on the first item with 2ND ENTER. Example: regression

Δ% — Percent change and compound interest (2ND 5) ↑ Contents

Gives the percent change between a starting value and an ending value, or the growth rate per period over several periods. Markup (profit over cost) is also done here.

• Clear 2ND CE|C → all go to 0, #PD goes to 1

Enter three and CPT the fourth. Example: percent change · growth

ICONV — Interest rate conversion (2ND 2) ↑ Contents

Converts between nominal and effective rates (concept).

• When what 12% a year compounded monthly really is, comparing the rates of two products on the same basis
• Clear 2ND CE|C → only NOM and EFF go to 0 (C/Y is kept — TI guidebook)

C/Y here is separate from C/Y in TVM (TI: worksheets do not affect each other). When you are done, leave with 2ND CPT (QUIT). Example: rate conversion

DATE — Dates (2ND 1) ↑ Contents

Gives the number of days between two dates, or the date and weekday some days after or before a date.

• Clear 2ND CE|C → dates go to 1990-12-31, DBD goes to 0 (ACT/360 stays)

With the US setting, dates are MM.DDYY (9.0403 = 2003-09-04). With EUR, they are DD.MMYY. Dates cannot be computed with the 360 method (Error 6). Range 1980–2079. Example: dates

PROFIT — Profit margin (2ND 3) ↑ Contents

If you know two of cost, selling price and margin (on price), it gives the third.

• Clear 2ND CE|C → all go to 0

For markup (profit over cost), use Δ%. Example: cost and price

BRKEVN — Breakeven (2ND 6) ↑ Contents

If you know four of fixed cost, variable cost, price, profit and quantity, it gives the fifth. The quantity where profit is 0 is the breakeven point.

• Clear 2ND CE|C → all go to 0

Example: breakeven

MEM — Memory (2ND 0) ↑ Contents

View and edit all 10 memories (M0–M9) that hold numbers for a while.

• Clear 2ND CE|C → all 10 memories go to 0

You can also do arithmetic on a memory, e.g. + 65 ENTER. Without opening the worksheet, use STO · RCL + digit.

FORMAT · RESET — Display format and reset ↑ Contents

FORMAT sets how numbers and dates are shown and the calculation order. RESET puts the whole calculator back to its starting state.

The FORMAT items are in this order: DEC → DEG/RAD → US/EUR → separators → Chn/AOS. Move with ↓, change with 2ND ENTER, and when you are done leave with 2ND CPT (QUIT). Example: switch to AOS = 2ND . ↓ ↓ ↓ ↓ 2ND ENTER 2ND CPT. Inside FORMAT, 2ND CE|C resets only the FORMAT settings. Full list: Settings and reset

6. Settings and reset ↑ Contents

All settings ↑ Contents

Settings are not cleared by CLR TVM, and they stay when you power off. But CLR WORK on the P/Y, BGN, FORMAT, BOND and STAT screens also resets the settings on that screen.

After you change a setting with keys, press 2ND CPT (QUIT) to leave the settings screen. If you do not, the next CPT you press is used on the settings screen, and the TVM calculation does not work.

In the SET tab you can pick only 0 · 2 · 4 · 6 · F decimals. For 1 · 3 · 5 · 7 · 8, use the keys.

Clear and reset commands ↑ Contents

Each command clears something different. Most cleared values stay in the LOG, so you can look at them and enter them again.

7. Side panel ↑ Contents

LOG — History ↑ Contents

Every key and result, line by line. Values removed with CLR TVM and similar also stay here, so you can look at them and enter them again (there is no restore button). Copy copies everything, Clear empties it.

REG — All stored values ↑ Contents

All stored values at a glance: the five TVM values, every cash flow (count / 32), ten memories and the number of statistics points. Use it when the value list is hidden on short phones.

CHART — Charts ↑ Contents

Cash flow bars · NPV curve with IRR · amortization over time · statistics scatter. Hover for values, Table for the numbers.

EXCEL — Working with Excel ↑ Contents

Export (Copy · CSV) · paste in (Load as CF / DATA) · the matching Excel formulas. Amortization interest and bond duration are calculated differently from Excel, so the last digits can differ slightly. Example: working with Excel

SET — Settings ↑ Contents

Change P/Y · C/Y · END/BGN · Chn/AOS · decimals · angle · date format · separators with a click. Orange means not the default. Exam preset sets exam settings (P/Y · C/Y 1, END, DEC F, AOS); Defaults restores the defaults. Theme: Ultramarine · Light, Green · Light, Ultramarine · Dark, Green · Dark (buttons show a colour swatch and name).

8. Install ↑ Contents

iPhone home screen ↑ Contents

1. Open drfaustcalc.com in Safari on your iPhone
2. Share (square with an up arrow) → Add to Home Screen → Add
3. Open DrFaustCalc from the home screen. It works without the internet (offline)

Values, settings and the log are stored separately on each device.

Mac app ↑ Contents

Applications → DrFaustCalc or Cmd+Space → "DrFaustCalc". Type on your keyboard right away; CSV files open a save dialog.

9. Troubleshooting ↑ Contents

Common mistakes (when the answer is wrong) ↑ Contents

• Old values from the last problem: they are marked old. Clear with CLR TVM / CLR WORK before a new problem. This does not clear settings (P/Y · C/Y · BGN), so also check the settings line.
• BGN left on: check for an orange BGN on the settings line.
• Copying the rounded display: hold the result to see all digits; Cmd+C copies the unrounded value.
• 2+3×4 gives 20: the default calculation order (Chn) works in the order you press. For multiplication first, switch to AOS or use parentheses (calculation order).

Error codes ↑ Contents

Press CE|C to clear an error and try again. The message line shows the cause in one line.

10. Glossary ↑ Contents

The labels on the calculator keys and display, in alphabetical order. Each row says in one line what it is. For details, follow the link in the Where column. When the same label is used in different places, it has separate rows (e.g. N in TVM and n in statistics).

Keys · functions · display labels ↑ Contents

Worksheet items ↑ Contents

App only (not on the physical calculator) ↑ Contents

↑ Contents · ← Back to the calculator