HP-12C Calculator Online
A faithful, free web clone of the Hewlett-Packard HP-12C — the gold-faced financial calculator that has been in continuous production since September 1981 and is still required equipment on the CFA exam in 2026. Authentic Reverse Polish Notation entry, the four-level stack with T-register replication, and the full Time-Value-of-Money solver, behaving exactly the way the real device behaves.
Output is for general illustration only and is not financial, investment, tax, or legal advice. See our Terms.
The 30-second tour: RPN, the stack, and how it feels
If you have never used Reverse Polish Notation, the muscle memory takes about ten minutes to acquire and then you never want to go back. The basic idea: numbers first, operator last. To compute 2 + 3, you key 2, then ENTER, then 3, then +. The display shows 5.00. There is no equals key on the HP-12C and there are no parentheses, because you do not need them — the order you type is the order things happen.
Under the hood, four numbers sit on what HP calls the operational stack, named X, Y, Z, and T from bottom to top. X is the value you see on the LCD. ENTER pushes X up the stack so the next number you type lands in a fresh X. After a binary operation like +, the stack drops: Y takes the value that was in Z, Z takes T, and T replicates itself. That last detail — T replicating instead of zeroing — is the famous HP behavior that lets you load a constant into the top of the stack and have it refill Y as you drop. The canonical test is to key 5 ENTER ENTER ENTER × × × and watch the display land on exactly 625.00 (which is 5⁴). If a calculator passes that test, the stack is working.
Once that clicks, long financial chains feel inevitable. There is no scratch paper, no half-finished expression that you have to remember to close. Each press resolves immediately into a value you can see.
Canonical test sequences (try them right now)
Every key on this clone has been verified against published HP-12C output for the following sequences. Tap the buttons above and watch the LCD — the display should match the right column exactly.
| Press | Display | What it tests |
|---|---|---|
2 ENTER 3 + | 5.00 | Basic RPN addition |
5 ENTER ENTER ENTER × × × | 625.00 | T-register replication on stack drop |
200 ENTER 25 % + | 250.00 | % keeps Y on the stack (5% of 200 = 50; 200 + 50 = 250) |
240 ENTER 60 %T | 25.00 | 60 is 25% of 240 |
100 ENTER 110 Δ% | 10.00 | 10% change from 100 to 110 |
2 ENTER 10 yx | 1,024.00 | Exponentiation |
360 n 0.5 i 200000 PV 0 FV f PMT | -1,199.10 | 30-year $200k mortgage @ 6% APR |
240 n 0.5 i 0 PV 100 CHS PMT f FV | 46,204.09 | $100/month into account at 0.5%/month for 20 years |
g 7 36 n 5 g i i 20000 PV 0 FV f PMT | -596.93 | BEG-mode 36-month lease at 5% APR on a $20k cap |
5 STO 0 CLx RCL 0 | 5.00 | Store and recall from register 0 |
A small thing worth knowing: the cyan g i shortcut (which divides X by 12, useful for turning an APR into a monthly rate) does not also store the result into the i register. The display will show the divided value but the TVM solver still has whatever was there before. Press unshifted i afterwards to actually store the rate. The real HP-12C works the same way.
What is and isn't implemented yet
Fully working: RPN entry, the four-level stack with T-replication, x⇄y swap, R↓ rolldown, CLx, CHS, EEX, the four arithmetic operators, yx, 1/x, all three percent variants, twenty STO/RCL registers, the entire TVM solver (n, i, PV, PMT, FV) in both END and BEG mode, and the g-shifted √x, ex, LN, INTG, FRAC, 12×, and 12÷.
Not yet implemented: cash-flow analysis (NPV, IRR, CFo, CFj, Nj), bond pricing (PRICE, YTM), depreciation (SL, SOYD, DB), the statistics registers (Σ+, Σ−, x̄, s, linear regression), date arithmetic (DATE, ΔDYS, D.MY, M.DY), and programming mode (P/R, R/S, SST, BST, GTO). Those keys are present on the layout for visual fidelity, but pressing them returns an error rather than guessing — nothing here will silently mislead you.
Frequently asked questions
What is RPN and why does the HP-12C use it?
Reverse Polish Notation puts the numbers first and the operator last: instead of typing 2 + 3 =, you press 2, ENTER, 3, +. The intermediate values live on a four-level stack, and every operation pulls its inputs from the stack and pushes the result back. There are no parentheses because you never need them — the order you key in is the order things happen. HP shipped the 12C with RPN in 1981 because, for long financial chains, it is genuinely faster and produces fewer mistakes than algebraic entry.
How do I solve a mortgage payment on the HP-12C?
Key in the five Time-Value-of-Money registers, then press the orange f shift followed by the one you want to solve for. For a 30-year $200,000 mortgage at 6% APR (0.5% per month), the sequence is 360 n 0.5 i 200000 PV 0 FV f PMT. The answer comes back as -1,199.10 — the negative sign means money flowing out of your pocket each month. The HP-12C uses the banker's cashflow sign convention: deposits are positive, withdrawals (and loan payments) are negative.
What is the four-level stack and the T-register?
The HP-12C holds four numbers at once in registers called X (the visible one), Y, Z, and T (top). ENTER pushes the X value up the stack so the next number you type lands in a fresh X. After a binary operation like +, the stack drops: Y receives Z, Z receives T, and T replicates itself. That T-replication is the classic stack trick — load 5 with three ENTERs, multiply three times, and you get 625 because the 5 in T keeps refilling Y as the stack drops.
What is the difference between END mode and BEG mode?
END mode (the default, set by g 8) assumes each payment happens at the end of its period — the convention for mortgages, car loans, and almost every consumer loan. BEG mode (set by g 7) puts the payment at the beginning of the period, which is how leases, rent, and most annuities-due are quoted. The BEGIN annunciator lights up on the LCD when you are in BEG mode. The math difference is one extra compounding period per payment, so BEG-mode payments are slightly smaller than the equivalent END-mode payments at the same rate.
Why is the real HP-12C still in production 44 years later?
HP introduced the 12C in September 1981 and has produced it continuously ever since — longer than any other calculator ever made. It survived because the CFA Institute, mortgage banking, and a generation of real-estate professionals built their muscle memory around its keys. Replacing it would mean retraining millions of fingers. The 30th-anniversary edition, the 40th-anniversary edition, and the current production unit are all visually identical to the original. The full story is in our article on why the HP-12C refused to die.
Is this clone exact?
The core engine is exact. We verified against canonical HP-12C test sequences including 5 ENTER ENTER ENTER × × × = 625 and a 30-year mortgage solving to exactly -1,199.10. Bond pricing, depreciation, statistics, cash-flow analysis, date math, and programming mode are not yet implemented — those keys currently return an error, by design, so nothing silently misleads you.
Does keyboard input work?
Yes. Digits, decimal, the four arithmetic operators (+ − × ÷), Enter, %, ^ (for yx), C / Backspace / Delete (for CLx), and Escape (to clear an armed shift) are all mapped. The shift keys themselves (f, g) and the financial keys (n, i, PV, PMT, FV) have to be clicked, because there is no clean keyboard mapping for them — but the basic arithmetic chain is fully typeable.