Water filter running-cost calculator

Enter the price of the correct replacement pack

Find the refill that matches your device before doing the arithmetic. A cheaper pack from another family cannot be made into a useful comparison by dividing it into more litres. Use the cartridge compatibility directory if the model or generation is uncertain.

Enter the amount you would actually pay for the selected pack, the number of cartridges and your expected filtered-water use per day. The MAXTRA PRO setting uses 28 days and 150 litres as maximum planning limits. For a different cartridge, select custom limits and copy the applicable figures from its current instructions.

Running-cost calculator

What will it cost to keep it supplied?

Use the current price of the exact replacement pack. MAXTRA PRO uses a maximum of 150 litres or four weeks, whichever comes first. For another cartridge, enter the limits on its pack.

Cartridge limitsBRITA MAXTRA PROEnter my cartridge's limits

Current pack price (£)Cartridges in the pack

Filtered water used per day (litres)

Time limit (days)Volume limit (litres)

Estimated annual cartridge cost

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Per cartridge

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Planning interval

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Equivalent cartridges / year

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Per litre used

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Enter the pack price to see your estimate.

An ongoing-use estimate over 365 days, using the earlier time or volume limit. Hardness can shorten service life. Round up cartridges when budgeting whole packs; allow separately for the jug, supplied filters, delivery and subscriptions.

The result updates as you change valid entries. Blank or invalid inputs clear the estimate so an old result is not mistaken for a new calculation. Use a consistent household consumption figure when comparing packs, and remember that local conditions can require earlier changes than the stated maxima.

What each result means

• Per cartridge: the pack price divided by its cartridge count.
• Planning interval: the earlier time limit or the time needed to reach the volume limit.
• Equivalent cartridges per year: 365 divided by that interval, expressed as ongoing use.
• Annual cartridge cost: the equivalent yearly use multiplied by the cost per cartridge.
• Cost per litre used: that annual cost spread over your expected consumption, shown in pence.

A decimal number of cartridges is useful for comparing an ongoing routine. It does not mean a retailer sells part of a refill. Use whole cartridges and the actual pack sizes when planning cash purchases, while keeping the fractional estimate for a like-for-like comparison.

Our analysis: how daily use changes cartridge value

Better Home Water calculated twelve usage scenarios from the two manufacturers’ published replacement schedules. The useful finding is that a cartridge’s advertised litre allowance can be a poor shortcut for cost at low daily use: the time limit can arrive while much of that allowance is still unused.

When does volume matter more than time?

Divide the rated litres by the maximum days to find the boundary. Below it, the time limit arrives first; above it, the volume limit does. MAXTRA PRO gives 150 ÷ 28 = 5.357… litres a day. Evolve+ gives 100 ÷ 30 = 3.333… litres a day. The displayed boundaries are rounded for reading, so use the full figures when calculating near the dividing point.

At 2L/day, the MAXTRA PRO model uses 56 litres in 28 days: 37.3% of 150 litres. Spreading the cartridge price over 56 litres instead of 150 makes its effective cost per litre 150 ÷ 56 = 2.68 times as large. The corresponding Evolve+ model uses 60 litres in 30 days, making its multiplier 100 ÷ 60 = 1.67. These multipliers describe each schedule; they do not establish which cartridge is cheaper at its actual price.

BRITA MAXTRA PRO: six daily-use scenarios

Inputs: 150 litres and 28 days, using the earlier limit. Manufacturer replacement guidance. 150 litres at the stated 10–12°dH hardness; harder water can shorten life.

Aqua Optima Evolve+: six daily-use scenarios

Inputs: 100 litres and 30 days, using the earlier limit. Manufacturer replacement guidance. Single-cartridge 30-day/100-litre planning schedule; follow the actual pack and device instructions.

*Compared with dividing the same cartridge’s unit price by all its rated litres. A multiplier of 1.00 means the volume limit is reached. At the exact boundary both limits coincide. Percentages describe use of the published allowance, not the amount of filtration media remaining.

What unit price gives the same annual cartridge spend?

Price alone can reverse the result. At 2L/day, the Evolve+ schedule needs fewer annual cartridge equivalents than the MAXTRA PRO schedule. At 4L/day, its smaller volume allowance is reached sooner and it needs more. The table holds daily use constant and calculates the Evolve+ unit price that would give the same ongoing cartridge spend as MAXTRA PRO.

For example, at 4L/day an Evolve+ cartridge would need to cost about 89.3% of a MAXTRA PRO cartridge’s unit price to give equal annual cartridge spend under these assumptions. Below that price it costs less in this model; above it, more. Calculate unit price from the complete pack and unavoidable delivery. Fit and the treatment purpose must be suitable before this comparison is useful; equal spend does not mean equal filtration or automatic interchangeability.

Method, assumptions and downloadable figures

1. Take the named cartridge’s published maximum time and volume limits.
2. For each fixed daily use, choose the shorter of maximum days or maximum litres ÷ litres per day.
3. Divide 365 by that interval for annual cartridge equivalents. Multiply by your pack price ÷ pack count for annual cost.
4. Divide rated litres by the litres used in that interval for the shortcut multiplier. For equal-spend unit prices, divide MAXTRA PRO annual equivalents by Evolve+ annual equivalents.

The underlying calculations keep full precision; tables round days and annual equivalents to two decimal places, and percentages to one. They assume constant consumption over 365 days, one cartridge per change and use up to the stated maximum. Earlier replacement reduces the interval and increases costs. BRITA’s 150-litre figure is conditional on its stated water hardness; it is not a guaranteed household yield. Paired-cartridge dispensers, interruptions, supplied starter filters, stock, whole-pack purchases, electricity, water charges and other stages are outside this comparison.

Any separate daily-throughput or operating limit in your appliance manual still applies. A shorter calculated replacement interval does not permit exceeding that limit; the higher-use rows are arithmetic scenarios, not approval for a particular device.

Download all twelve calculation rows and source links (CSV). The analysis uses no live retailer prices. Use the calculator above to substitute your actual pack price, consumption and any shorter applicable limits.

Worked examples using hypothetical prices

These prices are deliberately invented round figures, not current Amazon offers. They show why the same pack can have a different effective cost per litre in a different household.

In the first example, the household uses only 56 litres during a 28-day interval. Dividing £5 by a rated 150 litres would understate the cost of the water it actually uses. In the second example, higher consumption reaches 150 litres sooner: the annual spend rises even though the effective cost per litre is lower.

The third example uses a different schedule. It illustrates why a compatible-brand refill should be assessed with its own limits rather than inheriting the original cartridge’s figures. Lower calculated cost does not establish identical fit or filtration; those questions must already be settled.

Compare the two MAXTRA PRO types on equal terms

Use the current selected pack price for Pure Performance and Limescale Expert, holding consumption and applicable limits constant. This shows the cost difference for your household without treating the scale-focused type as a longer-lasting cartridge. Read the purpose comparison before deciding whether that purpose matters to you.

Use Evolve+ limits when comparing that family

For the Evolve+ pack discussed here, the stated planning figures are 30 days and 100 litres. Check the actual pack’s instructions and confirm any key needed for your jug in the Evolve+ compatibility guide.

Turn the estimate into a purchasing budget

A six-pack of cartridges changed every four weeks covers 24 weeks under that schedule, not half of every calendar year. Take care with phrases such as “six-month supply”: they can hide differences between a month, a four-week interval and a volume limit reached early.

An ongoing estimate of 13.04 cartridges does not map exactly to buying two six-packs. You may already have stock, receive cartridges with a new jug or need to buy another complete pack. Track opening stock and likely fitting dates, then round the purchase quantity to the packs actually sold. Spares carried into the next year are stock, not evidence that the annual-use formula is wrong.

Subscription and delivery checks

Include unavoidable delivery in the entered pack price. Compare a subscription using its continuing price and delivery conditions, rather than only an introductory discount. Check whether the delivery interval matches the replacement routine; regular deliveries can still build up excess stock or arrive after a high-use household runs out.

Store unopened refills according to the maker’s guidance and retain their identity. A very large bundle only helps when it is the right family, remains suitable to store and will be used. The genuine versus compatible guide covers the other purchase checks that a low unit price cannot answer.

Costs the calculator leaves out

This is a single-cartridge running-cost model. It excludes the container, installation, water charges, electricity, membranes, cleaning products and other filter stages. For a Doulton installation, for example, budget each pre-filter separately as explained in the replacement identification guide.

If your instructions specify calendar months, use a calendar reminder for the real change date. Any conversion into days for comparison is an estimate, not a reason to extend a manufacturer’s deadline. Revisit the inputs when your usage or pack price changes rather than treating one result as a permanent household cost.

If you are unsure what to budget for, define the taste or scale concern first. A softener or RO system has operating costs beyond a single sealed refill.

Electrical appliances add costs beyond cartridges. See Cube filter costs and the dispenser versus kettle energy comparison for the relevant schedules and an equal-volume calculation.

Questions before you buy

Sources and further reading

• BRITA cartridge FAQ
• Aqua Optima Evolve+ specification
• BRITA MicroDisc specification