A 3-ton central air conditioner in Mississippi costs about $114.11 in July and $486 a year at 15.06¢/kWh; an 8,000 BTU window unit about $23.81 in July.
At 15.06¢/kWh — Mississippi average, Jan–Aug 2026 (EIA). That is 17% below the U.S. average of 18.19¢.
| Efficiency | Per year | vs yours |
|---|---|---|
| SEER2 13.4 (min · North) | $519 | +$32.65 |
| SEER2 14.3 (min · South) | $486 | — |
| SEER2 15.2 (ENERGY STAR) | $457 | −$28.79 |
| SEER2 17 (ES average) | $409 | −$77.21 |
| Month | Full-load hours | 3-ton central | 8,000 BTU window |
|---|---|---|---|
| January | 7 | $2.81 | $0.59 |
| February | 6 | $2.10 | $0.44 |
| March | 22 | $8.18 | $1.71 |
| April | 39 | $14.73 | $3.07 |
| May | 129 | $48.87 | $10.20 |
| June | 237 | $90.03 | $18.78 |
| July | 301 | $114.11 | $23.81 |
| August | 285 | $108.03 | $22.54 |
| September | 184 | $69.92 | $14.59 |
| October | 58 | $21.98 | $4.59 |
| November | 10 | $3.74 | $0.78 |
| December | 4 | $1.64 | $0.34 |
DOE's room-AC test assumes 750 full-load hours a year for a typical U.S. home. We scale it by Mississippi's population-weighted cooling degree days (2,079 ÷ 1,216) and spread it over the months the same way: 1,282 hours a year. Your thermostat setting and insulation move this a lot — switch the calculator to your own hours if you know them.
3 tons = 36,000 BTU/h ÷ SEER2 14.3 = 2,517 W. × 1,282 h = 3,228 kWh × 15.06¢ = $486.
The full method, material data and tips are on the main air conditioner cost calculator page.