Air fryers became a sensation partly on the promise of slashing cooking bills, and there is truth in it, but also a fair amount of overstatement. An air fryer is essentially a small, fast fan oven, and its savings come from that smallness, not from any special efficiency.
Why it can save
A full-size oven has a large cavity to heat and takes time to come up to temperature, so cooking a modest portion in it wastes energy heating empty space. An air fryer heats a tiny chamber quickly and circulates hot air efficiently around the food, so for one or two portions it does the job in less time and far less energy. For chips, a couple of fillets or reheating, the saving over firing up the big oven is genuine.
When it does not save
The advantage shrinks or vanishes as the quantity grows. Cooking a large family meal in several small air-fryer batches can use as much energy as one ovenful, and a roast for six belongs in the oven. The air fryer wins on small, quick jobs and loses on big batch cooking, so it complements the oven rather than replacing it. Buying one will not cut your bills if you still use the oven for everything substantial.
What a session costs
A typical air fryer pulls one to two kilowatts but for a short time, so a fifteen or twenty minute cook costs only a few pence at usual electricity prices. Run your model's wattage and a realistic cooking time through the cost calculator to see your own figure. The headline saving against the oven is real for small meals, but it is pence per meal, not pounds, so set expectations accordingly.
Where it sits
Think of the air fryer as the right-sized tool for small, quick cooking, alongside the microwave for reheating and the oven for big batches. Used that way it genuinely trims cooking energy. Bought as a miracle that pays for itself in weeks, it will disappoint. As ever, match the appliance to the job and the savings follow.