Circuit Breaker Load Calculator

Calculate your home’s total electrical load and find out if your panel can support new circuits for an EV charger, hot tub, or addition.

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The interactive calculator for this tool is in development. In the meantime, use the cost guide and FAQs below to get your estimate.

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Why Use This Tool?

Before adding any large electrical load — EV charger, hot tub, addition, or major appliance — you need to know whether your existing panel has capacity. A licensed electrician will do a formal load calculation, but this tool gives you a preliminary answer before you make the call.

About This Tool

A residential electrical panel has a rated amperage (100A, 150A, 200A) that limits total connected load. The NEC (National Electrical Code) requires that the total calculated load not exceed 80% of panel capacity for continuous loads. This calculator estimates whether your panel has available capacity for a new large circuit.

How It Works

Enter your panel amperage

Found on your main breaker. 100A, 150A, or 200A are most common.

Enter your major loads

HVAC system, water heater, electric range, dryer, and any other 240V circuits.

Enter the new circuit you want to add

EV charger (40–50A), hot tub (50–60A), addition circuits, etc.

See your capacity result

The calculator tells you if you have headroom, are near capacity, or need a panel upgrade.

Cost Context

A load calculation determines if a panel upgrade is needed. If your panel has capacity, adding a 50-amp EV charger circuit costs $400–$900. If you need a panel upgrade first, add $1,500–$4,000. Knowing in advance prevents surprise upcharges.

Frequently Asked Questions

How do I know if my panel has enough capacity for an EV charger?

A 40-amp EV charger circuit requires 50 amps of panel capacity (125% rule for continuous loads). If your panel has available breaker slots and unused amperage, you likely have capacity. A licensed electrician should perform a formal NEC load calculation before installation.

What is the 80% rule for electrical panels?

The NEC requires that continuous electrical loads (loads running 3+ hours continuously) not exceed 80% of the circuit breaker rating. For a 40-amp breaker, the maximum continuous load is 32 amps. This is why a 40-amp circuit is used for a 32-amp EV charger.

This tool helps with:

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