Most people who stooze don't actually verify their interest is working. You put money on a 0% card, check your savings account occasionally, and assume it's accruing. But interest on 0% credit cards works differently from regular savings — and if you're not tracking it, you might never spot when something goes wrong.
This guide shows you how to build a dead-simple daily tracker that lets you see your interest accruing in real time, spot errors before they cost you money, and optimize when to rotate your balance between cards.
How Interest Actually Accrues on 0% Cards
Before you can track interest, you need to understand how it works on a credit card balance transfer or purchase card.
Interest accrues on your daily balance. If you have £5,000 on a card at 1.5% AER (Annual Equivalent Rate), you earn roughly £20.55 per year on that amount — or about 5.6p per day. But here's the key: once you spend that money and it leaves your savings account, the interest stops. You only earn interest on the balance you're actually holding on the card.
So if you transfer £5,000 on day 1 and spend it all by day 15, you earn interest for only 15 days, not the full year. That's why timing matters.
The second thing to understand: interest posts to your savings account on specific dates, not continuously. Your savings account provider (the lender offering the 0% card) typically calculates interest daily but pays it out monthly, quarterly, or annually depending on the account. You won't see 5.6p appear each day — you'll see a lump sum appear on the payout date.
This is where tracking breaks down. Most people don't know when their payout date is, so they never confirm the interest actually arrived.
Building Your Daily Tracker
You need three pieces of information to track properly:
1. Your opening balance and deposit date
When you transfer money onto your 0% card, record:
- The amount (e.g. £5,000)
- The date it posted (this is your day 1)
- The expected interest rate (check your 0% card offer — it varies)
2. Your expected daily interest
This is simple maths. If you're earning 1.5% AER on £5,000:
- Annual interest: £5,000 × 0.015 = £75
- Daily interest: £75 ÷ 365 = £0.205 per day
Create a simple spreadsheet with columns:
| Date | Balance | Days Held | Expected Interest | Actual Interest | Notes |
|---|---|---|---|---|---|
| Oct 24 | £5,000 | 1 | £0.21 | Transfer posted | |
| Oct 25 | £5,000 | 2 | £0.42 | ||
| Oct 26 | £4,500 | 3 | £0.63 | £500 withdrawn |
3. Your payout date
Check your savings account terms. Interest typically posts on:
- The last day of the month
- The anniversary of your opening date
- A fixed date quarterly (e.g. 31 March, 30 June, 30 September)
Mark this date in red. This is when you'll verify whether the interest actually arrived.
Spotting When Interest Goes Wrong
When your interest payout arrives, compare the actual amount to your expected total. There are four common reasons it might be lower:
You withdrew money early. If you planned to hold £5,000 for 90 days but withdrew £2,000 on day 45, you've lost interest on that £2,000 for the remaining 45 days. Your tracker should have flagged this. Recalculate: you earned interest on £5,000 for 45 days, then £3,000 for 45 days.
The 0% period didn't start when you thought. Some 0% offers have a delay — money transferred today doesn't start earning until next month. Check your account terms. If this happens, your expected interest will be too high until the 0% kicks in.
Interest is being debited by fees or charges. Rare, but possible. Check your statement for annual fees or other charges that might offset your interest.
The interest rate changed. Some 0% cards advertise a tiered rate: 1.5% for the first three months, then 0.5% afterwards. Your tracker needs to reflect this change on the date it kicks in.
If your actual interest is within 5p of your expected amount, you're fine — minor rounding differences are normal. If it's more than 5p short and you can't identify why, contact the lender's customer service.
Rotating Money for Maximum Accrual
Once you have your tracker working for one balance, the system gets more powerful. Here's why: if you hold £5,000 for 90 days, you earn about £18.75. But if you rotate money between two cards, you can extend the earning period.
For example:
- Day 1–45: Hold £5,000 on Card A
- Day 46: Transfer that money to a regular savings account, transfer £5,000 fresh onto Card B
- Day 91: Transfer Card B money to savings, transfer another £5,000 onto Card A
Your tracker now has three separate earning periods. Each earns roughly £9.38, but the total period covered is 135 days instead of 90, and you've kept earning the whole time.
This only works if:
- You have multiple 0% cards (or a 0% purchase card plus a balance transfer card)
- Each card's 0% period is long enough to complete the rotation
- You can actually afford to keep moving the money around
If you're serious about stoozing, your tracker becomes the heartbeat of your whole strategy. It tells you when to rotate, how much each rotation earns, and whether you're actually making money or just pushing cash around.
Common Questions
Does my 0% interest count towards my Personal Savings Allowance? Yes, most of it does. Basic-rate taxpayers can earn up to £1,000 interest tax-free each year. Higher-rate taxpayers get £500 free. This interest counts against that allowance. Check your tax code and keep receipts of your payout statements to prove the amounts to HMRC if needed.
Can I set a phone reminder for my payout date? Absolutely. Set a recurring reminder one week before the payout date so you have time to check whether the interest arrived. If it doesn't show up on the actual payout date, you can contact the lender while the transaction is still fresh.
What happens to my interest tracker if I move my savings to a different bank? It still works. You're tracking the interest earned on your 0% card, not the savings account receiving it. The balance column in your tracker stays the same; the interest still posts to whichever account you nominated.
Do I need a sophisticated Excel template or can I use a note-taking app? A simple note-taking app works. The critical columns are: balance, days held, and expected interest. If you want to get fancy, add a column for actual interest so you can compare. But honestly, pen and paper works if you're holding just one balance.
What if my 0% period ends partway through my holding period? Your interest rate drops to the APR (typically 18–22%) on day one after the 0% ends. Your tracker needs to split into two calculations: interest at 0% for the period before the cutoff, and interest at the higher rate after. Most of the time, you'll want to move the money off the card before that happens.
Next steps: Choose a 0% card from our current offers, set your payout date reminder, and start tracking from day one. The difference between tracking and not tracking is the difference between knowing you're earning money and just hoping you are.