The Thirty Per Cent Solution: Fancy Dress for People Who Would Rather Not

There's a particular kind of invitation that arrives with a cheery little line at the bottom. Fancy dress encouraged! Theme: 80s! Come as your favourite decade! And there's a particular kind of person who reads that line and feels their entire personality quietly leave the room.

If that's you, this is for you. Not to convert you into someone who owns a morph suit, but to hand you a strategy that lets you walk in, enjoy the party, and not spend the evening explaining what you're meant to be.

The rule, in short

A thirty per cent nod to the theme beats a hundred per cent costume almost every time.

A hundred per cent means a hired outfit you've spent forty pounds on, a wig that itches, shoes you can't dance in, and a trip to the loos every hour to fix something. Thirty per cent means you wear clothes you actually like, add one or two deliberate details, and are visibly making an effort without being visibly uncomfortable.

Here's the thing nobody says out loud: nobody is checking. At a party, people register a look for about three seconds and then go back to the crisps. What they remember is whether you seemed up for it, which is why a considered half-effort lands better than a reluctant full one.

What the thirty per cent actually looks like

Choose your ordinary outfit first — the jeans, the dress, the shirt you'd wear to a pub lunch. Then add exactly one piece that says yes, I read the invitation. Two if you're feeling generous.

• 80s night. Your usual jeans and a plain white tee, plus a wide belt, oversized blazer and a single pair of neon hoop earrings.
• Halloween. All black, plus a tiny plastic spider brooch from a pound shop and a slick of dark lipstick.
• Cowboy or cowgirl hen do. Denim, boots you already own, and a neckerchief tied at the throat. Fringe optional.
• Festive work do. Whatever you'd normally wear, plus a sparkly top or a scarf with tinsel running through it.
• Black tie with a twist. Your own dress, plus elbow-length gloves or a velvet hair ribbon.
• Decades party. Pick the one decade whose silhouette you already like and lean on jewellery rather than clothing — a chunky plastic bangle says sixties far more cheaply than a dress does.

Notice the pattern? The costume is doing the work of an accessory, not an outfit. You're giving the group something to point at and say oh, she's an angel without committing to a tutu.

Use colour as your shortcut

The fastest way into a theme is a colour palette, and it's the trick that costs nothing. A green and red dress at a Christmas party requires no explanation. All white for a summer garden party reads as on theme without a single prop. Black and gold for a New Year's do does the job on its own.

If the theme is a specific character or era and you don't want to dress up, find the colour that's most associated with it and wear that. Effort, registered. Costume, avoided.

The one prop in the handbag

Here's an insurance policy. Take one small, packable item with you — a packet of stick-on moustaches, a sprig of tinsel, a feather boa that folds to nothing — and leave it in your bag. If you arrive and find you're the only one not dressed up, out it comes and you're instantly in on the joke. If everyone else has gone subtle too, it stays in the bag and no one is any the wiser.

This is genuinely the most useful thing you can do for party anxiety: give yourself a plan B that fits in a coat pocket.

Where to get the bits without spending much

Charity shops are unbeatable for this sort of dressing. You're not looking for a costume — you're looking for a single loud necklace, a velvet scarf, a pair of earrings shaped like something absurd, a waistcoat in a colour no one would wear by choice. Buy with an eye on whether it works with the clothes you already own, not whether it's funny on the hanger.

Supermarket clothing ranges and the high street also do cheap seasonal accessories in the run-up to Halloween and Christmas, and they're the sort of thing that gets marked down in the first week of November. Buy then, keep in a box, and you've got the next four themed invitations covered.

One more thing: check the back of your own wardrobe before you buy anything. Almost everyone owns something slightly ridiculous — a sequinned top from a wedding, a pair of gold boots, a waistcoat from a phase in 2013. That's your prop. It's already paid for.

When it's fine to opt out

Sometimes the honest answer is no costume, and that's allowed. Here's how to tell.

If the invitation says optional, take it at its word. If it's a work do and you're not sure how seriously people are taking it, ask one colleague. If you're travelling straight from a shift, or you've got a baby and a bag that already weighs more than you do, or the whole thing is causing genuine dread rather than mild eye-rolling — wear something nice and turn up.

What you shouldn't do is opt out loudly. There's a difference between not dressing up and making a performance of not dressing up. If the host has gone to the trouble of picking a theme, they're not asking you to love it; they're asking you to be a good guest. Turning up in a decent outfit with a smile and a bottle of something is being a good guest.

And if you do feel a bit bare, tie a ribbon round your wrist, put a flower in your hair, or wear the one bright thing you own. Thirty per cent is always enough. It's the party you're there for, not the fancy dress.