The bags are full, the costumes are wilting and the living room floor is about to disappear under a landslide of sweets. Welcome to the most important fiscal event of the year: the Halloween candy tax.

In many families, the grown-ups claim a small share of the Halloween haul. Done badly, it's a negotiation that ends in tears. Done well, it's one of the funniest traditions of the year, a running joke the whole family is in on. Here's the Parental Revenue Service's guide to doing it well.

What is the candy tax?

The candy tax is a playful family tradition: after trick-or-treating, the candy is counted and sorted, and a small portion is collected by the household's grown-ups. It's part joke, part portion control and part excuse to sit on the floor together sorting chocolate by type.

The Bureau's version comes with paperwork. The Parental Revenue Service, a deliberately silly parody with its own whimsical look, issues an official Candy Tax Assessment that records the haul, applies the household rate, notes any deductions and stamps the result. It isn't affiliated with, and doesn't imitate, any real government agency.

Agree the rules before the count

The single most effective way to avoid a meltdown is to agree the rules before the bag is opened. Children are surprisingly reasonable about taxation when they've helped set the rate. Talk it through on the walk home, or even before you head out.

A few common frameworks:

• The flat tax: one piece per bag, or one per grown-up, whatever the size of the haul.
• The small percentage: a modest share of the total, counted out together.
• The favourite-type levy: grown-ups claim every one of a particular kind, ideally one the children don't love.
• The voluntary contribution: children choose what to give, and the PRS thanks them formally for their generosity.

Deductions, credits and exemptions

This is where the fun really starts. A good tax system rewards good behaviour, and the PRS offers a generous menu of deductions. Brushing teeth without being asked might earn a reduction. Sharing with a sibling could qualify for a family credit. A homemade costume might be worth an exemption on one favourite chocolate.

Deductions turn a one-way collection into a game, and they keep the focus on the things you'd like to encourage. They're also a wonderful opportunity for extremely official language. “Your application for a Dental Hygiene Credit has been approved” never fails to get a laugh.

Running the count

Lay a towel or blanket on the floor and tip out the bags. Sorting is half the fun: by type, by colour, by favourite, by “will trade”. Younger children love counting; older ones enjoy tallying the totals and working out the tax.

When the count is done, file the assessment. Print the form, fill in the details and present it with ceremony. A rubber stamp, a red pen or a dramatic signature makes it official. Then collect the agreed tax, ideally with a receipt and a handshake.

If you'd like to keep some candy out of circulation for a while, this is also a good moment to set a portion aside for later in the week, presented as the Bureau's Candy Savings Scheme.

Swaps, trades and allergy exchanges

Some families prefer a trade to a tax: part of the haul is swapped for something else, like a book, a small toy or an outing. The Bureau's Candy Exchange Receipt records these trades properly, which helps the deal feel fair and final.

Trades are especially useful for children with food allergies. Candy containing allergens can be swapped for safe treats or small toys, and an official receipt turns what might feel like a loss into a good deal. Many families with allergies make the trade the main event of the night.

Whatever you trade for, keep it generous. The goal is for your child to feel they got a great bargain.

Keeping it kind

The candy tax works because it's a joke the child is in on. A few principles keep it that way:

• Never take the favourites without agreement.
• Keep the rate small and predictable.
• Offer plenty of deductions, and grant them generously.
• Laugh at the paperwork together.
• Never use candy as a threat or punishment. The PRS deals in good humour, not fear.

Parties and classrooms

The candy tax works as a party game, too. Hand out Candy Tax Assessments at a Halloween party and let children audit each other's bags for silly deductions, or give every guest a Costume Inspection Certificate on arrival. Teachers sometimes use the forms as a light-hearted maths activity: counting, sorting and calculating a pretend tax, with no real candy changing hands.

A quick safety sort

While you're sorting, it's sensible to check wrappers and set aside anything unwrapped, opened or unfamiliar. Watch for small hard sweets and other choking hazards if you have little ones, and keep an eye on allergens. A quick check keeps everyone safe and lets the PRS get back to its important work.