Cash ISA vs Premium Bonds — Which is Better for Your Savings?

Both Premium Bonds and Cash ISAs offer tax-free returns on your savings. Here’s how to choose between them.

Quick Comparison

Feature	Cash ISA	Premium Bonds
Returns	Guaranteed interest	Prize draw (variable)
Current rates	4-5% AER	4.65% prize fund rate
Tax	Tax-free	Tax-free
Annual limit	£20,000	N/A
Total limit	Unlimited over time	£50,000
Access	Instant (most)	1-2 working days
Minimum	Varies (often £1)	£25
Provider	Banks, building societies	NS&I only

How Cash ISAs Work

Guaranteed Returns

You deposit money and earn interest at an advertised rate.

Deposit	Rate	After 1 Year
£10,000	5.00%	£10,500
£10,000	4.50%	£10,450
£10,000	4.00%	£10,400

You know exactly what you’ll earn.

Tax-Free Interest

Situation	ISA Benefit
Any taxpayer	All interest tax-free
Higher/additional rate	Most valuable (no tax on what would be taxed at 40%+)

Annual Allowance

Tax Year	ISA Allowance
2025/26	£20,000
Previous year’s ISA	Doesn’t count against new allowance
Total in ISAs	Unlimited over time

If you’ve used ISAs for 20 years at £20,000/year, you could have £400,000+ tax-free.

How Premium Bonds Work

Prize Draw System

Instead of interest, your bonds enter a monthly prize draw:

Prize	Odds Per Bond
£1,000,000	1 in 50+ billion
£100,000	1 in 10+ billion
£50,000	1 in 5 billion
£25	Much higher
Nothing	Most bonds

Prize Fund Rate

Current Rate	What It Means
4.65%	Total prizes = 4.65% of all bonds
Not guaranteed	NS&I can change it
Distribution varies	Some win big, many win nothing

Expected Returns Reality

Holding	Expected Annual Return	Reality
£1,000	£46.50	Might win £0-£100+
£10,000	£465	Might win £100-£800 typically
£50,000	£2,325	Should win consistently but variable

Larger holdings = more consistent returns due to more bonds in each draw.

Returns Comparison

Guaranteed vs Variable

£10,000 Savings	Cash ISA (5%)	Premium Bonds
Year 1 expected	£500	£465 (but variable)
Year 1 possible	£500	£0-£1,000+
Certainty	100%	0%

Over Time

Investment Horizon	ISA Advantage	Premium Bonds Advantage
1 year	Certainty	Potential upside
5 years	Compound interest	Million-pound chance
20 years	Known outcome	Tax-free growth, prizes

Tax Comparison

Cash ISA Tax Treatment

Taxpayer	ISA Interest	Outside ISA
Basic rate	Tax-free	First £1,000 free (PSA)
Higher rate	Tax-free	First £500 free (PSA)
Additional rate	Tax-free	No PSA — all taxed

Premium Bonds Tax Treatment

Taxpayer	Prize Tax
Basic rate	Tax-free
Higher rate	Tax-free
Additional rate	Tax-free

Both are equally tax-efficient — no tax at all on returns.

Access and Flexibility

Cash ISA Access

ISA Type	Access
Easy access	Instant withdrawal
Notice ISA	30-90 days notice
Fixed rate	Locked for term

Premium Bonds Access

Action	Timeframe
Request withdrawal	Online or phone
Money received	1-3 working days
No penalty	Ever

Premium Bonds: always flexible, no penalties.

Investment Limits

Cash ISA Limits

Rule	Limit
Per tax year	£20,000
Per provider	Usually no max
Total lifetime	Unlimited
Transfers	Allowed between providers

Premium Bonds Limits

Rule	Limit
Minimum purchase	£25
Maximum holding	£50,000
Per person	£50,000 total
Joint holding	Not available

Once you hit £50,000, you can’t buy more Premium Bonds.

Who Should Choose Cash ISA?

Situation	Why Cash ISA
Want guaranteed returns	Know exactly what you’ll earn
Have more than £50,000	ISA has no upper limit
Want best current rates	Top ISAs may beat Premium Bonds
Need money for specific date	Certainty matters
Higher rate taxpayer	Tax-free certainty valuable

Who Should Choose Premium Bonds?

Situation	Why Premium Bonds
Enjoy the prize draw	Entertainment value
Already used ISA allowance	No annual limit
Want NS&I government backing	100% secure
Large lump sum	More consistent prizes
Risk-tolerant	Happy with variable returns

Using Both Together

Example Strategy

Account	Amount	Purpose
Cash ISA	£20,000	Guaranteed 5% = £1,000/year
Premium Bonds	£30,000	Fun + ~£1,400 expected prizes
Total	£50,000	~£2,400 tax-free

Benefits:

• £1,000 guaranteed from ISA
• Lottery-style excitement from Premium Bonds
• Some chance of big win
• All 100% tax-free

FSCS Protection Comparison

Account	Protection
Cash ISA	FSCS: £85,000 per bank
Premium Bonds	HM Treasury: 100% backed

Premium Bonds offer unlimited government backing; ISAs are protected up to £85,000 per banking licence.

When Premium Bonds Underperform

Small Holdings

Amount	Issue
£100	Might win nothing for years
£500	Very inconsistent
£1,000	Still highly variable

You need £5,000+ for reasonably consistent prizes.

Prize Fund Rate Changes

NS&I adjusts the prize fund rate based on Bank of England rates:

If Interest Rates Fall	Premium Bonds
Prize fund rate drops	Fewer/smaller prizes
ISA rates drop	Your fixed ISA rate unchanged

Locked-into a good ISA rate beats variable Premium Bonds if rates fall.

Current Best Rates

Top Cash ISAs (March 2026)

Provider	Rate	Type
Trading 212	5.10%	Easy access
Chip	4.75%	Easy access
Zopa	4.65%	Easy access

Premium Bonds

Metric	Current
Prize fund rate	4.65%
Odds per £1 bond	21,000 to 1 (monthly)

Cash ISAs currently offer slightly higher guaranteed rates.

Making the Decision

Choose Cash ISA If:

Priority	ISA Advantage
Certainty	Guaranteed returns
Long-term maximisation	Compound growth
Large savings (>£50k)	No upper limit
Best current rate	May beat Premium Bonds

Choose Premium Bonds If:

Priority	Premium Bonds Advantage
Government backing	100% secure
Million-pound chance	Life-changing potential
£50,000+ savings	After ISA allowance
Fun/excitement	Prize draw psychology

Choose Both If:

Situation	Split Approach
Have £30,000+	ISA for guarantee, PB for fun
Like variety	Best of both worlds
Uncertain about future	Hedge your bets

Summary

Factor	Cash ISA	Premium Bonds
Best for certainty	✓
Best for upside		✓
Best for £50,000+	✓
Best backing		✓ (Treasury)
Current return	~5% guaranteed	4.65% variable
Tax status	Tax-free	Tax-free

For most savers, Cash ISAs offer better value due to higher guaranteed rates. But Premium Bonds make sense for those who’ve used their ISA allowance, want 100% government backing, or enjoy the prize draw experience.