Tools
Heating Oil Calculator: How Long Will My Oil Last?
By the Hill & May team
Updated 2026
If an oil-fired Aga or range cooker shares a tank with your boiler, running dry is the expensive mistake: a cold cooker, a cold house and a rushed order. The sum is simple once you know three numbers: how much oil is in the tank, how much you can actually draw (the outlet sits above the base, and sludge collects at the bottom), and how many litres a week you burn. The figure usually quoted for a two-oven oil Aga left on is around 40 litres of kerosene a week, so a 1,000 litre tank at half full, keeping 100 litres back as a reserve, runs a cooker on its own for about ten weeks. Enter your own figures below to get the weeks left, the day to order by, and what filling up would cost.
How long will your heating oil last?
How the sum works
The calculator turns your gauge reading into litres (capacity multiplied by the percentage), takes off the reserve you cannot or should not draw, then divides what is left by your total weekly use. The run-out date is today plus that many days; the order-by date is the run-out date minus your delivery lead time. The refill cost is the room left in the tank, multiplied by your price per litre.
Two things make the answer less exact than it looks. First, many tank gauges are rough, and on a horizontal cylinder the gauge does not move in a straight line with the volume, so a dipstick reading against the maker's chart beats a guess. Second, a boiler's use swings with the weather; if you enter a summer figure in November you will run out sooner than the date shown. Measure your real weekly use with two readings a week apart and the forecast tightens up quickly.
Topping up an oil Aga tank
Do not order more than the room shown: the tanker driver needs space, and a tank that is overfilled can spill through the vent. If your refill is small, compare the per-litre price against a bigger order; on our heating oil price per litre page the gap between 300 and 900 litre orders was only about 4p a litre in October 2026. For where a tank can go and when it needs a bund, see oil tank rules for an oil-fired Aga, and for the yearly bill, Aga running costs per year.
