In the short run, an EV's energy cost is roughly 30–50% lower than petrol per kilometre. Charging at home on residential rates usually runs about one-quarter to one-third of petrol cost, even though public fast charging is pricier.
But EVs typically cost more to buy than a petrol car in the same segment, and they still depreciate faster for now because battery technology is changing quickly. The break-even point usually lands in year 3–5 if you drive a lot (above 15,000 km/year).
Don't guess — compare the 5-year cost of an EV and a petrol car on identical specs.