It is HP's longest and best-selling product and is considered the de facto standard among financial professionals.

[4] Its popularity has endured despite the fact that a relatively simple but iterative process such as amortizing the interest over the life of a loan, a calculation that modern spreadsheets can complete almost instantly, can take over a minute with the HP-12C.

The 1977 October edition of the HP Journal contains an article by Roy Martin, the inventor of the simple method of operation used in HP financial calculators, which describes, in detail, the mathematics and functionality built by William Kahan and Roy Martin that is still used today.

[2] The calculator's part number and physical appearance didn't change except for a "Rev 2" plate on the bottom side.

and Royal Consumer Information Products, Inc. released a minor revision of the HP 12C without "Hewlett-Packard" on the frontplate and with a screw added to the battery compartment cover.

[16] The HP 12c Platinum is similar in appearance and functionality to the 12C, and is designed to mimic the 12C whilst extending its capabilities in various aspects.

The calculator was introduced in 2003, is visibly distinguished by its silver-colored upper half as opposed to the gold-colored plate on the original 12c.

It was equipped with a Sunplus SPLB20D2[1][18] with a 6502 core, larger memory (for up to 30 CFj registers[17] and 400 program steps) and more built-in functions.

[19] The first HP 12c Platinum version (F2231A) did not have parentheses, which often led to awkward key sequences to solve problems in algebraic mode.

The firmware changes increased the ROM size beyond the capabilities of the original processor, so it was replaced by the Generalplus GPLB31A (still with 6502 core),[1] which is also faster.

In 2022, alongside the latest revision of the original 12C, Moravia and Royal also released a mostly cosmetic update of the 12c Platinum, with the words "Hewlett-Packard" removed from the frontplate, subtle adjustments to the layout and contact information on the rearplate, and a screw added to the battery compartment.

[15] By design, the HP-12C rounds up the number of payments to the next integer, which produces meaningless results when calculating fractional periods.

Deviating from the HP original, these calculators feature a dot-matrix display, switchable fonts and clock speeds, and, based on a Silicon Labs CP2102 converter chip,[27] they come with a USB (Mini-B)[28] serial interface to exchange data with a PC etc.