How long will heating oil last?
It depends on how fast your house burns it, and only your own readings can tell you that. Two dips a week or two apart give you a daily rate. Divide the oil you have left by that rate and you have the number of days.
This page is about how fast you burn it. For how long oil keeps in storage, InspectAPedia cites a shelf life of 18 to 24 months for No. 2 oil without additives.
The math
used = first reading − last reading + deliveries in between
per day = used ÷ days between the readings
days left = (oil now − oil you count as empty) ÷ per day
Readings come as inches on a stick, so turn each one into gallons first with the chart for your tank. Inches are not gallons: on a rounded tank the top and bottom inches hold less than the middle ones.
A worked example
A 275 gallon tank standing up. On 2026-01-04 the stick reads 30 in, which is 190.1 gal. On 2026-01-18 it reads 21 in, 127.0 gal. No delivery came in between.
- Used in 14 days
- 190.1 − 127.0 = 63.1 gal
- Per day
- 63.1 ÷ 14 = 4.51 gal
- Counted as empty (10% of 267.9 gal)
- 26.8 gal
- Usable oil left
- 127.0 − 26.8 = 100.2 gal
At $5.97 a gallon (Maine's statewide average on October 5, 2026) those two weeks cost $376.81, about $26.91 a day.
Open this example in the calculator and change the numbers to yours.
Days left by daily use
Usable gallons down the side, gallons burned per day across the top. Rounded down to whole days.
| Gallons | 2/day | 3/day | 4/day | 5/day | 6/day | 8/day |
|---|---|---|---|---|---|---|
| 50 | 25 | 16 | 12 | 10 | 8 | 6 |
| 100 | 50 | 33 | 25 | 20 | 16 | 12 |
| 150 | 75 | 50 | 37 | 30 | 25 | 18 |
| 200 | 100 | 66 | 50 | 40 | 33 | 25 |
| 250 | 125 | 83 | 62 | 50 | 41 | 31 |
Why the date moves
The estimate carries your past rate forward. Heating use follows the weather, so a cold snap after your readings burns oil faster than the average says, and a mild spell slower. A rate measured in October will run long in January.
Heating engineers handle this with degree days: how far each day's average outdoor temperature fell below a base (65 °F in the US). Gallons used divided by degree days over the same stretch gives a rate per degree day that holds up better across the season. If you track degree days for your area, that number is worth writing down with each reading. The heating oil use per day page shows the math with tables.
Hot water from the same boiler uses oil all year, so summer readings show that part on its own.
Tips for better readings
- Dip at the same spot each time, and after a delivery once the truck has gone.
- Write down the delivery amount from the ticket. Add it in the calculator with its date so the gallons it added are not counted as negative use.
- The longer the gap between the first and last reading, the steadier the rate.
The calculator does all of this for up to six readings and three deliveries, and keeps them in a link you can bookmark.
Heating with propane? The gauge reads in percent instead of inches, and the 500 gallon propane tank chart runs the same math for it.
Once you know your gallons per season, the heating fuel cost comparison shows what the same heat costs from propane, gas, a heat pump or wood at your prices.