Switching to an electric vehicle offers significant savings on fuel, but understanding the logistics of "filling up" is different from a gasoline car. This EV Charging Calculator helps you estimate exactly how long it will take to charge your vehicle's battery to a specific level and how much that session will cost based on your local electricity rates.
To get an accurate estimate, you'll need to know your battery's total capacity (in kWh), your current charge level, your charger's output speed (in kW), and your electricity cost.
Calculate Your Charge Session
function calculateEVCharge() {
// Get inputs
var batterySize = parseFloat(document.getElementById("evBatterySize").value);
var chargerPower = parseFloat(document.getElementById("evChargerPower").value);
var currentCharge = parseFloat(document.getElementById("evCurrentCharge").value);
var targetCharge = parseFloat(document.getElementById("evTargetCharge").value);
var energyCost = parseFloat(document.getElementById("evEnergyCost").value);
var resultDiv = document.getElementById("evCalcResult");
// Validation
if (isNaN(batterySize) || isNaN(chargerPower) || isNaN(currentCharge) || isNaN(targetCharge) || isNaN(energyCost)) {
resultDiv.style.display = "block";
resultDiv.innerHTML = "Please enter valid numeric values for all fields.";
return;
}
if (batterySize <= 0 || chargerPower <= 0 || energyCost < 0) {
resultDiv.style.display = "block";
resultDiv.innerHTML = "Battery size and charger power must be greater than zero. Cost cannot be negative.";
return;
}
if (currentCharge 100 || targetCharge 100) {
resultDiv.style.display = "block";
resultDiv.innerHTML = "Charge percentages must be between 0 and 100.";
return;
}
if (targetCharge <= currentCharge) {
resultDiv.style.display = "block";
resultDiv.innerHTML = "Target charge level must be higher than current charge level.";
return;
}
// Calculations
var percentageNeeded = targetCharge – currentCharge;
var kWhNeeded = batterySize * (percentageNeeded / 100);
// Assume charging efficiency (approx 90% for L2, slightly different for DCFC but 90% is a safe average estimate for AC)
// We divide by efficiency because you pull MORE from the wall than ends up in the battery.
var efficiencyFactor = 0.90;
var kWhPulledFromGrid = kWhNeeded / efficiencyFactor;
// Time calculation (Hours = kWh needed / charger kW)
// Note: Charging slows down past 80%, this is a linear estimate.
var totalHoursDecimal = kWhNeeded / chargerPower;
// Convert decimal hours to hours and minutes
var hours = Math.floor(totalHoursDecimal);
var minutesDec = (totalHoursDecimal – hours) * 60;
var minutes = Math.round(minutesDec);
// Handle edge case where rounding minutes equals 60
if (minutes === 60) {
hours++;
minutes = 0;
}
// Cost calculation
var totalCost = kWhPulledFromGrid * energyCost;
// Display Result
resultDiv.style.display = "block";
resultDiv.innerHTML =
"
" +
"Note: Estimates assume ~90% charging efficiency. Actual time may vary, especially as the battery approaches 100% charge, as charging speeds typically decrease.";
}
Understanding the Inputs
To use the calculator effectively, here is a breakdown of the required inputs:
Total Battery Capacity (kWh): This is the size of your EV's "fuel tank," measured in kilowatt-hours. Common sizes range from 40 kWh (Nissan Leaf) to over 100 kWh (Tesla Model S Plaid, Lucid Air).
Charger Power Output (kW): How fast the charger can deliver energy.
Level 1 (Household outlet): typically 1.2 kW to 1.4 kW.
Level 2 (Home wallbox or public AC): typically 3.6 kW to 11 kW (7.2 kW is very common).
DC Fast Charging (Level 3): typically 50 kW to 350 kW.
Electricity Cost ($ per kWh): This is your residential utility rate, or the cost at a public charging station. The average residential rate in the US is around $0.16 per kWh, but it varies significantly by region and time of use.
The "Charging Curve" Factor
It is important to note that this calculator provides a linear estimate. In reality, EV batteries do not charge at a constant speed from 0% to 100%.
Most EVs charge fastest when the battery is low (e.g., below 50%). Once the state of charge reaches roughly 80%, the vehicle's onboard battery management system significantly reduces the charging speed to protect battery health. Therefore, charging from 80% to 100% often takes much longer than charging from 20% to 80%.