What your air conditioner really costs to run
From the BTU of your split unit and its SEER to the kilowatt hours it actually draws, with the cost per hour, per month and per season, two units side by side and the price of one degree.
Type the BTU of your split unit (or its kW of cooling) and its efficiency: the tool tells you what an hour, a night, a month and a whole season cost.
Your unit
Picking a class fills SEER with the lowest value that class guarantees. If the exact SEER is printed on the label, type it in by hand: it is the number that drives the whole calculation. The kW input is on the rating plate of the unit, not on the energy label, and it only serves to show how much of your supply the unit takes.
How you use it and what you pay for power
Average load is the share of its capacity the unit actually delivers: once the room is at temperature, an inverter slows down and an on off unit cycles. Counting running hours as full power hours is the mistake that makes air conditioning look twice as expensive as it is.
How to use it
The first tab starts from the unit you own (BTU or kW of cooling plus a class or a SEER) and gives you the cost per hour, per day, per month and per season. The second puts two units side by side with the same hours and the same load, and if you type how much more the new one costs it works out how many seasons it takes to pay back. The third turns one degree on the thermostat into money. Hours, days, average load and the price of electricity live in the blue box and apply to all three tabs.
Why the BTU on the box are not the watts you pay for
The 9,000 BTU/h of a split unit are cooling capacity, the heat it removes from the room: one kilowatt is 3,412 BTU/h, so that is 2.64 kW of cooling. The energy you buy is that divided by efficiency, and with a SEER of 6.1 it becomes roughly 430 watts drawn on average. Treating those 2.64 kW as if they were electricity consumption gets the bill wrong by a factor of four, and it is the most common mistake online. For the same reason a generic appliance calculator is not enough here: it asks for watts drawn, and an air conditioner label simply does not carry that number.
SEER, the classes and the kWh printed on the label
SEER is the seasonal ratio between cooling delivered and electricity consumed, and it already accounts for modulation, cycling and standby. The classes come from EU delegated regulation 626/2011: A+++ from 8.50 up, A++ from 6.10, A+ from 5.60, A from 5.10, B from 4.60, C from 4.10, D from 3.60, E from 3.10, F from 2.60 and G below that. Nothing below class B has been sold new in Europe since 2014 under ecodesign regulation 206/2012, so the bottom classes only show up on old machines (for G, which has no lower bound, the menu offers 2.50). The same rules define the kWh per year printed on the label, which are rated capacity times 350 hours divided by SEER. Those 350 are the equivalent full load hours of an average European cooling season, and that is why the result tells you how many times the label your own usage is worth.
Load factor, the term almost everyone forgets
Hours with the unit switched on are not hours at full power. Once the room is at temperature an inverter drops to 20 or 30% and an on off unit cycles, so the cooling actually delivered is a fraction of the nameplate. The tool multiplies hours by days by load to get equivalent full load hours, which is the quantity you are entitled to divide by SEER. Something between 40 and 70% describes normal use of a properly sized room; 100% is the limit case of an undersized unit that never catches up, and the result says so when you pick it.
What a degree is worth, and what this calculation cannot know
Turning the thermostat up works on two fronts. The heat coming in through walls, windows and air changes is proportional to the gap between outside and inside, so with 31 degrees outside, moving from 24 to 25 cuts the gap from 7 to 6 degrees, a seventh off that share; internal gains (people, lights, appliances, humidity) do not change, which is why the tool asks you how much each part weighs. On top of that the compressor gains around 2.5% efficiency for every degree of warmer evaporation. Together they give the 8% per degree everyone quotes when it is 35 outside, and 12% when it is 31: the percentage is not a constant. All of this stays an estimate rather than a meter reading: the latent load of dehumidification is not modelled and it matters a lot in humid summers, SEER is measured on an average European climate so real consumption is higher in the south, and time of use tariffs are ignored. The range of kW drawn at full power comes from typical catalogue EER figures, not from a standard: copy the value from the rating plate and the calculation becomes exact.