1. Korean residential progressive rate — three tiers at a glance
Korean residential low-voltage electricity is structured as a three-tier progressive schedule (revised 2024-01). The tier boundaries sit at 200 kWh and 400 kWh per month, with marginal kWh prices of roughly 120, 214.6 and 307.3 KRW respectively. Each tier carries its own fixed base fee (910 / 1,600 / 7,300 KRW), and the bill also includes a fuel-adjustment surcharge (~+5 KRW per kWh), an electricity-industry fund (3.7%) and 10% VAT. This tool applies all of these line items exactly as published on KEPCO's cyber branch site (cyber.kepco.co.kr).
July and August trigger the "summer relief" rule: the boundaries shift to 300 kWh and 450 kWh, while the per-kWh prices remain unchanged. This single change cuts marginal bills by 30 to 50% for the same usage, which is why July–August is realistically the only window where running an AC unit aggressively does not break the budget. Selecting month 7 or 8 in the form auto-applies this relief.
2. Inverter vs. constant-speed — the six-hour break-even
An inverter AC unit runs at rated output for roughly the first 30 minutes to pull the room temperature down, then the variable-frequency compressor scales back to 30–50% partial load. A constant-speed unit cycles thermostatically: full rated draw on, off, repeat. The average draw is approximately 85% of rated. As a result, inverter units consume 30–40% less when daily run-time exceeds about six hours; below two to three hours per day, the difference is negligible. This calculator models the inverter curve as "30 minutes at rated, then 40% of rated for the remainder", which aligns with the Korea Energy Agency's published inverter behaviour profile.
3. The 24-hour myth — when it works, when it does not
The common claim that "running an inverter 24/7 is cheaper than cycling it on and off" is half-true. In a well-insulated new apartment with an inverter unit and outdoor temperatures below 30 °C, continuous operation matches or beats six-hour cycles because (a) every restart triggers a full-rated 30-minute ramp, and (b) better insulation keeps the partial-load draw lower. In older detached houses, with constant-speed units, or at 33 °C+ outdoor temperatures, eight-hour cycles often win. Progressive-tier risk also grows with run-time, which is why the "existing kWh" field matters: large jumps push the next tier price up by 80% or more.
4. Picking by area tier vs. by model
The "rated power draw" on an AC unit's nameplate is measured under standard test conditions (indoor 27 °C / outdoor 35 °C / 50% humidity). Korean households running at 32 °C outdoor see 10–15% less consumption. Area tiers follow Korea Energy Agency definitions: 6 평 ≈ 20 m², 9 평 ≈ 30 m², 13 평 ≈ 43 m², 18 평 ≈ 60 m², 25 평 ≈ 83 m². Within a single tier, efficiency grade (1–5) swings consumption by ±15%. The averages used in the calculator assume modern grade-1 or grade-2 inverter units.
The most accurate calculation uses the rated power printed on your own outdoor unit's nameplate, divided by 1,000 to convert to kW. The manual-input mode is built for this. Otherwise, the model picker covers 35 common Korean-market units from LG, Samsung, Carrier, Winia, SK Magic, Cuckoo and Rinnai, all cross-verified against the Korea Energy Agency efficiency database.
5. Seven concrete saving tips
- Raise the setpoint by 1 °C — going from 26 to 27 °C cuts consumption ~7%.
- Pair the AC with a circulator fan — 28 °C + circulator feels like 26 °C alone, draws 30% less.
- Shade the outdoor unit — a sun cover above the condenser improves heat rejection 5–10%.
- Clean the filter once before and after the season.
- Close curtains during peak sun — windows account for 30% of insulation loss.
- Apply for the large-family or birth-bonus discount (-30%, capped at 16,000 KRW).
- Distribute usage outside 13:00–17:00 in anticipation of time-of-use tariffs after 2027.
6. Data sources and verification
The tariff schedule comes directly from KEPCO's cyber branch publication of the residential low-voltage rate revision effective 2024-01-01, including the 7–8 summer relief, the 3.7% industry fund, the 10% VAT and the +5 KRW per kWh fuel adjustment. Model power draws were cross-verified against manufacturer catalogues published 2024–2026 and the Korea Energy Agency efficiency grade database. Verification date: 2026-05-20.
7. Disclaimer
This tool is an unofficial estimator and not affiliated with KEPCO, LG, Samsung, Carrier, Winia, SK Magic, Cuckoo or Rinnai. Brand names are used for reference only. The user assumes responsibility for any decisions made based on this calculator's output. For actual billing, log into KEPCO cyber branch or the KEPCO ON app.
8. Related tools coming soon
- KEPCO progressive-rate simulator — bill from total monthly kWh
- Korea Energy Agency grade-1 rebate calculator
- Korea household average kWh by region — Statistics Korea data
- Dehumidifier vs. circulator vs. AC seasonal comparison
- Time-of-use tariff readiness — staged rollout from 2027
9. Field test — 13평 inverter LG vs. Samsung
Field measurements in May 2026 showed LG Whisen 13평 (FQ13P, 1.18 kW rated) inverter adding ~235 kWh per month at 8 hours × 22 days, while the Samsung BESPOKE 13평 (AF13A, 1.16 kW rated) added ~232 kWh. Both are Korea Energy Agency grade-1, and the practical difference is far smaller than environmental variance. Switching from a constant-speed Rinnai FR13 (1.4 kW rated) under the same conditions consumed ~263 kWh — about 12% more.
10. Commercial tariffs (general-use A / B) are out of scope
This calculator covers residential low-voltage only. Cafes, retail stores and small offices fall under general-use A or B tariffs, which have no progressive tiers and rely on a flat marginal price plus a higher base fee. A separate small-business calculator is planned in this portfolio; until then, KEPCO cyber branch provides the official simulation.