Free Complex Number Calculator — Arithmetic, Polar Form & Conjugate

A complex number calculator performs arithmetic operations on complex numbers — addition, subtraction, multiplication, division, conjugation, magnitude, and polar form conversion — with full step-by-step solutions showing FOIL expansion, intermediate products, and results in both rectangular (a + bi) and polar (r∠θ) form.

Complex numbers appear throughout engineering, physics, signal processing, and advanced mathematics. Operations like multiplication require careful FOIL expansion and the rule that i² = −1, while division involves multiplying by the conjugate. This calculator handles all of that automatically while showing you exactly how each result is derived.

• Add and subtract - Combine real parts and imaginary parts separately for quick complex arithmetic
• Multiply complex numbers - See the full FOIL expansion with i² = −1 substitution and simplification
• Divide complex numbers - Multiply numerator and denominator by the conjugate, then simplify step by step
• Find the conjugate - Flip the sign of the imaginary part for use in division or other operations
• Calculate magnitude - Compute |z| = √(a² + b²) to find the distance from the origin in the complex plane
• Convert to polar form - Get r and θ so you can express complex numbers as r∠θ or r(cos θ + i sin θ)

• Multiplication requires FOIL and i² = −1 - You must expand four terms and then substitute i² = −1 to simplify, which introduces sign errors if you're not careful
• Division is a multi-step process - Dividing complex numbers means multiplying both numerator and denominator by the conjugate of the denominator, expanding, and simplifying separately
• Polar conversion needs trigonometry - Converting between rectangular and polar form requires computing arctangent and handling quadrant adjustments
• Sign tracking gets tricky - With negative real parts, negative imaginary parts, and i² flipping signs, it's easy to lose track of positive and negative terms

Enter the real and imaginary parts of each complex number, then select your operation. For multiplication, the calculator performs FOIL expansion (First, Outer, Inner, Last), applies i² = −1, and combines like terms. For division, it multiplies by the conjugate and simplifies. Every operation also outputs the result in polar form (magnitude and angle).

The step-by-step breakdown shows each intermediate product, the i² substitution, the combination of real and imaginary parts, and the final answer in both rectangular and polar notation.

Example

To multiply (3 + 4i) × (1 + 2i), the calculator expands: First = 3×1 = 3, Outer = 3×2i = 6i, Inner = 4i×1 = 4i, Last = 4i×2i = 8i². Substituting i² = −1 gives 8(−1) = −8. Combining: (3 − 8) + (6i + 4i) = −5 + 10i. The polar form is approximately 11.18∠116.57°.

• Electrical engineering - Multiply impedances in AC circuit analysis where voltages and currents are complex quantities
• Signal processing - Add complex Fourier coefficients when combining frequency components
• Quantum mechanics - Perform arithmetic on complex probability amplitudes and wave functions
• Control systems - Analyze transfer functions involving complex poles and zeros
• Mathematics coursework - Verify homework on complex arithmetic, polar conversions, and conjugate operations

• All major operations - Add, subtract, multiply, divide, conjugate, magnitude, and polar form in one tool
• Full FOIL breakdown - See every intermediate product in multiplication so you can follow or learn the process
• Dual output format - Results displayed in both rectangular (a + bi) and polar (r∠θ) form automatically
• Division made clear - The conjugate multiplication technique is shown step by step, demystifying complex division
• Free and unlimited - Perform as many complex number calculations as you need at no cost

What operations are supported?

The calculator supports addition, subtraction, multiplication, division, conjugation, magnitude (absolute value), and polar form conversion. These cover all standard complex number operations encountered in math and engineering courses.

How do I enter complex numbers?

Enter the real part and imaginary part separately in the provided fields. For example, for 3 + 4i, enter 3 as the real part and 4 as the imaginary part. Negative values are fully supported.

What is polar form?

Polar form expresses a complex number as r∠θ, where r is the magnitude (distance from the origin) and θ is the angle measured from the positive real axis. It's especially useful for multiplication and division, which become simpler in polar notation.

Can I use purely real or purely imaginary numbers?

Yes. Enter 0 for whichever part is absent. For a purely real number like 5, set the imaginary part to 0. For a purely imaginary number like 3i, set the real part to 0.

What is the difference between unary and binary operations?

Binary operations (add, subtract, multiply, divide) require two complex numbers. Unary operations (conjugate, magnitude, polar form) operate on a single complex number. The calculator adjusts its input fields based on the operation you select.

Is this calculator free to use?

Yes. The complex number calculator is completely free with no usage limits, no sign-up required, and no restrictions on the number of calculations you can perform.