Understanding your result
The headline is the leftover paint, bought minus used, and the sub-line says how much of it to keep and how much to deal with. The three figures split it: keep for touch-ups, return (the unopened cans, up to the surplus) and give away or dispose of.
The table repeats the arithmetic: bought, used, leftover, the touch-up share with its one-quart minimum, the surplus, the returnable and the rest, and the shelf life once opened for the paint type. The notes do the practical part: how to store the touch-up jar, whether it will last until the next repaint, where unopened cans go, and the disposal route for latex or oil.
Leftover is the price of rounding up, and the place to cut it is before you buy. The can size optimizer finds the combination of pails, gallons and quarts with the least waste for a price; the paint cost calculator shows what the leftover cost; and the quantity converter turns a leftover in litres or quarts into the units on the can.
How we calculate this
The touch-up share is a share of what the job used, because a larger job has more wall to scuff. The one-quart floor exists because less than a quart dries out in a large can and is hard to brush from; a quart in a full quart can, or a few smaller jars, keeps far better than a gallon can a quarter full. The unopened cans are counted as returnable only out of the surplus, so the touch-up paint is never the can you drove back to the store.
The shelf life is the typical figure for opened, well-sealed paint kept above freezing: about two years for latex and five for oil-based. The disposal routes follow the US EPA’s guidance for household paint and the PaintCare stewardship programs in the states that have them. The can sizes and leftover guide covers storage and buying in more detail, and the can sizes reference lists the containers.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Touch-up share | 10% of the paint used, at least 1 quart | Site judgement; enough for normal scuffs and repairs |
| Shelf life, opened latex | about 2 years | Manufacturers’ storage guidance for sealed, unfrozen cans |
| Shelf life, opened oil-based | about 5 years | The same guidance; oil paint skins over but keeps longer |
| Returns | unopened, untinted cans with a receipt | Typical US home-improvement store policy; tinted paint is usually not returnable |
| Latex disposal | dry out and trash where allowed, or PaintCare drop-off | US EPA household paint guidance; PaintCare state programs |
| Oil disposal | household hazardous waste collection | US EPA household hazardous waste guidance |
Assumptions last reviewed October 8, 2026.
The planner does not know your local rules, which decide whether dried latex can go in the trash; check your city or county waste pages. It does not handle lead-containing paint from before 1978, which is a different matter under the EPA’s rules and not a leftover question.
Two worked examples
A bedroom repaint with a little over
3 gallons bought, 2.3 gallons used, 10% for touch-ups, latex, the next repaint in five years.
- Leftover: 3 − 2.3 = 0.7 gallons, or 2.8 quarts
- Keep: the larger of 2.3 × 10% = 0.23 gallons and one quart, so 1 quart
- Surplus: 2.8 − 1 = 1.8 quarts to give away or dry out
The five-year plan is longer than latex keeps once opened, so the note says to expect to re-buy a touch-up quart after year two, from the colour code on the label.
Oil enamel with a spare unopened gallon
5 gallons bought, 3 used, one gallon still sealed, oil-based, next repaint in three years.
- Leftover: 2 gallons; keep: 3 × 10% = 0.3 gallons, or 1.2 quarts
- Surplus: 2 − 0.3 = 1.7 gallons
- Return: the sealed gallon; give away or take to hazardous waste: 0.7 gallons, or 2.8 quarts
A larger job, 10 gallons bought and 7.5 used with 2 gallons unopened, leaves 2.5 gallons: keep 3 quarts, and the whole 1.75 gallon surplus fits inside the unopened cans, so it all goes back to the store.
Where to find your inputs
Paint bought. The receipt, or the can list from the quantity calculator you used.
Paint used. Bought minus what is in the cans; tip a can and estimate by the level, or weigh it (latex is about 11 lb a gallon full; the paint weight calculator converts).
Unopened. Sealed cans you never opened. Tinted counts as unopened for storage but usually not for returns.
Years to the next repaint. Five to ten for most interior rooms, less for hallways and children’s rooms.
Common mistakes
- Keeping the touch-up paint in a big can a quarter full. The air in the can skins it over. Decant into a small, full container.
- Storing paint in a garage that freezes. Frozen latex goes lumpy and is gone.
- Pouring latex down the drain. It is still a pollutant, and it clogs pipes.
- Putting oil paint in the trash. Hazardous waste collection only.
- Throwing away the label. The colour code is how a store remakes it years later.
- Returning the touch-up can by mistake. Set it aside before the return trip.
Questions people ask
- How much paint should I keep for touch-ups?
- About 10% of what the job used, and never less than a quart. A room that took 2.3 gallons leaves you a quart, enough for scuffs, nail holes and the patch behind a picture you moved. Keep it in a small, full, sealed container labelled with the room, the colour, the sheen and the date.
- How long does leftover paint last?
- Opened latex paint, sealed well and kept from freezing, is usually good for about two years; oil-based paint for about five. Unopened cans last longer. If the paint smells sour, has lumps that will not stir out or has separated into a rubbery skin, it has gone off.
- Can I return unopened paint?
- Untinted, unopened cans usually go back with the receipt. Custom-tinted paint usually does not, because the store cannot sell it again. Ask before the drive; the planner counts the unopened cans as returnable only up to the surplus you do not need for touch-ups.
- How do I dispose of latex paint?
- Never down a drain. Small amounts can be dried out with kitty litter or a paint hardener and, where local rules allow, put in the household trash with the lid off. Several US states have a PaintCare program with drop-off sites at paint stores that take leftover paint for free.
- How do I dispose of oil-based paint?
- At a household hazardous waste collection, which most counties run on set days or at a permanent site. Oil-based paint and the solvents used to clean it up must never go in the trash or down a drain.
- What if I want touch-up paint years from now?
- Write down the brand, the product line, the colour name or code and the sheen from the can label, and photograph it. Any store with that line can mix a fresh quart from the formula. The planner flags it when the next repaint is further away than the paint will keep.