The Best Circuit Simulation Software in 2026

LTspice is free, fast, and backed by Analog Devices' model library; it is the tool most power-supply and analog engineers reach for first, and vendor models for regulators, op-amps, and MOSFETs are widely available for it. QSPICE (Qorvo) is a newer free simulator from LTspice's original author, with modern C++ and Verilog behavioral blocks. ngspice is the open-source engine underneath KiCad and many other tools. On the commercial side, Cadence PSpice (with a free PSpice for TI edition), NI Multisim, and TINA add vendor ecosystems and, in some cases, digital co-simulation.

What none of these do is turn the simulated circuit into a board. That is fine when simulation is the deliverable; it is a redraw when the board is.

Falstad CircuitJS animates current flow and voltage in the browser and is the fastest way to build intuition for RC filters, transistor stages, and logic. CircuitLab pairs a clean editor with a simulator and is common in coursework. Treat both as teaching tools: ideal components, quick answers, no manufacturing path.

The practical middle ground is simulating inside the EDA tool, on the same schematic that becomes the PCB. ProtoFlow runs a built-in SPICE engine locally: it generates the netlist from your schematic, includes models for common diodes, transistors, MOSFETs, and an ideal op-amp, auto-creates sources from your power symbols when you have not placed one, and plots transient, AC, DC sweep, and operating-point results in an interactive waveform viewer. Because ProtoFlow also drafts the schematic from a plain-English description and attaches real parts, the loop of "describe → simulate → adjust → lay out" stays in one free app, and the result still exports as a native KiCad project.

KiCad integrates ngspice directly, with the full analysis set and the ability to attach vendor SPICE models to symbols. It is more work to set up models than a dedicated simulator, but the payoff is the same: no redraw between the simulation and the board.

Learning: Falstad. Precision analog and power with vendor models: LTspice or QSPICE. Course or documentation work: CircuitLab. Anything that will become a PCB: simulate where you design — ProtoFlow for the fastest free start (and AI-drafted schematics), KiCad for the deepest free ngspice setup. Commercial teams already inside Cadence or NI ecosystems: PSpice or Multisim.