Right, before we get to the version of this that people actually do, let’s deal with the version I’d heard about initially where you start at 1p then double each day!
What Happens If You Genuinely Double a Penny Every Day
Start with 1p on day one. Double it every day after that. Sounds gentle, doesn’t it. Here’s where it actually goes.
| Day | Amount you’d need to save that day |
|---|---|
| 1 | £0.01 |
| 10 | £5.12 |
| 20 | £5,242.88 |
| 25 | £167,772.16 |
| 30 | £5,368,709.12 |
By day 30 you’d need to find over five million pounds, on that single day, just to keep the pattern going. By day 60 the number has more digits than most calculators can display. There is no version of “double a penny every day for a year” that exists outside of a maths classroom. Whatever challenge you’re thinking of, and whatever version you remember doing, it almost certainly was not this one.
What I think you’re remembering is the 1p Savings Challenge, which works very differently, and is genuinely something people complete every year. Let’s look at that instead, because it’s the one worth talking about.
The 1p Savings Challenge, Properly Explained
The actual challenge adds a penny each day, rather than doubling. Save 1p on day one, 2p on day two, 3p on day three, and so on, all the way through to day 365. The amounts creep up gently rather than exploding.
| Point in the year | Daily amount | Running total |
|---|---|---|
| End of January | around 31p | £4.96 |
| Halfway (day 183) | £1.83 | £168.36 |
| End of December | £3.65 | £667.95 |
£667.95 is the total if you start on 1 January and complete all 365 days. It’s been doing the rounds since around 2015, and Monzo now runs an automated version inside its app, complete with a £10,000 prize draw for anyone who completes the full year. There are also 2x and 4x versions for people who want to be more ambitious, reaching £1,335.90 and £2,671.80 respectively. Worth knowing the 4x level needs over £400 in December alone, which tells you everything about how this challenge behaves over time.
What I Genuinely Like About It
The concept is a good one. January asks almost nothing of you, under £5 for the whole month, so there’s no barrier to starting. It builds a daily habit at a point when habits are cheap to form, and by the time the amounts start to feel real, you’ve already been doing it for months without noticing. As a way of getting someone who has never saved anything to start, it’s genuinely well designed.
Where It Falls Apart
The problem is the second half of the year, not the first. December alone asks for around £108, compared to under £5 in January. That’s not a gentle ramp by that point, it’s a noticeable jump in exactly the month when most people’s spending is already stretched the furthest. The challenge that started by asking nothing of you ends by asking quite a lot, at the worst possible time.
I tried this properly, and the bit that got me wasn’t the total. £667.95 over a year is a perfectly sensible amount to save. It was the shape of it. Easy months lulled me into not thinking about it, and then the harder months arrived all at once, right when Christmas was already eating into everything else.
What I Do Instead
Once I’d worked out the total, the rest was simple. £667.95 over 12 months is £55.66 a month, or £12.85 a week if you’d rather think of it that way. So I set up a standing order for that flat amount, the same figure every month, and left it alone.
It’s a slightly harder ask in January than the original challenge, and a noticeably easier one in December. But it gets you to the same total, £667.95 over the year, without the sting at the end. The same logic I use for subscriptions applies here too. Anything that runs automatically in the background, on a fixed amount, tends to actually happen. Anything that requires you to remember what day of the year it is and find an increasingly specific number of pennies tends not to.
If You Already Budget Properly, This Might Not Be For You
Here’s the bit that I think gets missed in most write ups of this challenge. The whole pitch rests on the idea that you’ve got loose change and small unaccounted for amounts lying around that you won’t miss. That’s true for a lot of people, and genuinely useful if it’s true for you.
But if you’ve already gone through the process of getting a clear picture of where your money goes, there often isn’t a pile of unaccounted for pennies sitting around waiting to be redirected. Every pound is already doing something. In that case, the challenge isn’t really finding hidden money, it’s deciding in advance to set some aside and adjusting everything else around it. Which is a perfectly good thing to do, it’s just a different exercise to the one the challenge implies it is.
If you do want to see what £667.95 could become over a few years rather than just sitting in a current account, my savings interest calculator is worth a few minutes.
Did Anyone Actually Finish It?
I’m genuinely curious about this. Over a million people apparently joined Monzo’s version in 2025. If you’ve done the 1p challenge, in any form, I’d love to know how far you actually got. Did you make it to day 365, or did December do what it did to me? And if you completed it, did it actually change anything afterwards, or was it just £667.95 that arrived and then sat there? Let me know in the comments, I’m putting together a follow up on what happens after these challenges end, and real experiences would be far more useful than anything I could work out on a spreadsheet.
For more on building habits like this without the nasty surprises, my spending habits guide rounds up the rest of what’s on the site so far.