To reduce cost, the HP-25 omitted the HP-65's magnetic card reader, so it could only be programmed using the keyboard.

Nearly all buttons had two alternative functions, accessed by a blue and yellow prefix key.

The HP-25 used a 10-digit red LED display and was the first calculator to introduce the "engineering" display option, a denormalized mantissa/exponent format where the exponent is always a multiple of 3 to match the common SI prefixes, e.g. mega, kilo, milli, micro, nano.

The owner's manual came with 161 pages in four colors and contained many mathematical, scientific, navigational and financial programming examples.

A version adapted to support an additional backward-facing display manufactured by Educational Calculator Devices named EduCALC 25 GD existed as well.