Aquarium Running Cost Calculator

This aquarium running cost calculator works out what a fish tank costs to run per day, per month and per year. Enter the heater power and the share of time it is on, the filter power and the light power and hours. It shows the total cost and a breakdown for the heater, filter and light, so you can see where the money goes. It starts with the UK price cap unit rate, and you can type your own tariff.

Quick answer: An aquarium costs the kWh used by its heater, filter and light times your unit rate. A tank with a 100 W heater on 30% of the time, a 10 W filter and a 15 W light on for 8 hours uses about 1.08 kWh a day, about 28p a day or £103.75 a year at 26.32p. The heater is usually the biggest part of the cost.

How Is Aquarium Running Cost Calculated?

Add up the daily kWh for each part, then multiply by your unit rate and by 365 days.

• Heater: watts x 24 hours x the share of time it is heating
• Filter: watts x 24 hours, as it runs all the time
• Light: watts x the hours it is on each day

Divide each by 1,000 to turn watt hours into kWh. An aquarium heater has a thermostat, so it only switches on when the water drops below the set temperature. In a warm room it may run for a small part of the day, and in a cold room much more. The 30% default is an example. Some tanks also have air pumps, chillers or UV sterilisers, which you can add to the filter power.

How Do You Use the Aquarium Calculator?

1. Enter the heater power and the share of time it is on.
2. Enter the filter power.
3. Enter the light power and the hours it is on each day.
4. Choose a price preset or enter your unit rate.
5. Read the yearly cost and the breakdown for each part.

How Much Does a Fish Tank Cost to Run?

A small tropical tank often costs tens of pounds a year to run, and a large one can cost a few hundred, mostly because of the heater.

The 26.32p unit rate is the Ofgem price cap average for October to December 2026. You can check the latest figure on the Ofgem energy price cap page.

Why Does Room Temperature Matter So Much?

The heater makes up the gap between the room temperature and the water temperature your fish need, so a colder room means a much bigger bill.

With a 100 W heater, changing the heating share from 15% to 50% changes the yearly cost from about £69 to about £150 in this calculator. A tank in a warm living room uses far less heater energy than the same tank in a cold conservatory or garage. Cold water tanks without a heater cost only the filter and light. Always set the temperature to suit your fish, not to save money.

Worked Example: A Large Tropical Tank

Example: a large tropical aquarium has a 200 W heater that runs about 40% of the time, a 25 W external filter and a 30 W LED light on for 10 hours a day. The unit rate is 26.32p.

• Heater: 200 W x 24 h x 40% = 1.92 kWh a day
• Filter: 25 W x 24 h = 0.6 kWh a day
• Light: 30 W x 10 h = 0.3 kWh a day
• Total: 2.82 kWh a day, about 74p
• Per year: £270.91

Here the heater is about two thirds of the cost. A tight fitting lid, keeping the tank away from cold walls and windows, and an insulated background panel all help the heater run less.

Tips to Cut Aquarium Running Costs

Small changes help without affecting your fish.

• Fit a lid or cover to reduce heat lost through evaporation.
• Keep the tank away from draughts, windows and outside walls.
• Use a heater with a reliable thermostat and check it with a separate thermometer.
• Use LED lighting on a timer.
• Clean filters as the maker advises so pumps run efficiently.

For other devices left on all day, the standby power cost calculator shows what small loads add up to.

Aquarium Running Cost FAQs

Checked October 2026. Source: Ofgem energy price cap. Heater heating share is an example; use your own figure.