Salary-Sacrifice Into Your Workplace Pension First — A SIPP Top-Up Only Wins If Your Employer Hands You a Dud Fund

Salary sacrifice works by reducing your gross pay before tax and National Insurance are calculated. You agree with your employer to give up £100 of monthly salary; £100 goes straight into your workplace pension; your take-home pay drops by £100 minus the tax and NI you would have paid on that £100.

For the 2026/27 tax year a basic-rate employee pays 20% income tax plus 8% Class 1 National Insurance on earnings between £242 and £967 a week. Combined, that's a 28% marginal rate on the sacrificed portion. So £100 of sacrificed salary reduces your take-home by £72. A higher-rate employee pays 40% tax plus 2% NI = 42% combined, so £100 sacrificed costs them £58 net.

Now the SIPP comparison at equal net cost. The SIPP gets 20% basic-rate relief at source: pay £72 net and the provider grosses it to £90. A higher-rate taxpayer claims an extra 20% via Self Assessment, getting a £14.50 cash refund on a £72.50 SIPP contribution — that refund hits your bank account, it doesn't go into the pension unless you actively reinvest it.

The gross delta on a £100 monthly contribution: salary sacrifice £100 in the pot, SIPP £90 in the pot (basic-rate) or £87 of total benefit (higher-rate, including the cash refund). You're 11% to 15% ahead before a single fee is paid.

Here's where the spread widens. When you sacrifice salary, your employer also saves their 15% employer National Insurance on the sacrificed amount (the secondary Class 1 rate rose from 13.8% to 15% in April 2025 alongside a drop in the secondary threshold). On a £100 monthly sacrifice that's £15 a month the employer no longer owes HMRC.

Many employers — particularly large-cap PLCs and FTSE-listed firms — share some or all of that 15% saving back into your pension. Check your scheme rules: a partial rebate of 50% adds £7.50 a month to your £100, taking the gross to £107.50. A full pass-through (more common in pre-2025 schemes that haven't been recalibrated) puts £115 in your pot per £100 sacrificed.

Versus the SIPP at the same net cost (£72 in): you're now putting £107.50–£115 in the workplace pot vs £90 in the SIPP. That's 19-28% more invested capital from day one. Over 25 years at 5% real growth, an extra £15 a month compounds into roughly £8,400 of additional pot — and that's at the conservative pass-through assumption.

No SIPP fee saving in the universe of mainstream platforms covers that gap. A 0.15% AMC delta on a £100k pot is £150 a year. The NI advantage is worth £180-£400 a year on a £200/month contribution, depending on the rebate generosity and your tax band.

The SIPP-first crowd's main lever is fund fees. Let's price it honestly. A modern auto-enrolment default fund — Aviva's My Future Focus, Aegon's BlackRock LifePath, Scottish Widows' Pension Portfolio Two — sits between 0.25% and 0.45% all-in. Older private-sector schemes that haven't been recalibrated since 2018 can run 0.55-0.80%. Public-sector schemes (NHS, USS, LGPS) are defined-benefit so this comparison doesn't apply.

A cheap SIPP holding a global tracker isn't free either. Vanguard's UK platform charges 0.15% platform fee (capped at £375/yr) plus 0.18% on its LifeStrategy or FTSE Global All Cap — total 0.33% on small pots, dropping below 0.20% on six-figure balances. AJ Bell, InvestEngine and Interactive Investor are all in the 0.25-0.45% all-in range for a tracker-only portfolio.

On a £100,000 pot held for 25 years at 5% gross growth:

• Workplace default at 0.45% AMC: ending balance ≈ £337,400 (drag ~£11,900 vs zero fees)
• Cheap SIPP at 0.30% AMC: ending balance ≈ £349,800 (drag ~£8,300 vs zero fees)
• Fee delta over 25 years: ~£12,400

Now compare to the salary-sacrifice NI boost on the same 25 years of contributions. Sacrificing £200/month at basic rate with an 8% employee NI saving and a half-rebated 7.5% employer NI saving adds roughly £37 a month to the pot versus a SIPP at the same net cost. Over 25 years that's £11,100 of extra contributions, which at 5% real growth compounds to ~£23,000 of additional pot.

The NI advantage (£23,000) is nearly double the fee disadvantage (£12,400). The SIPP only wins when your workplace AMC pushes 0.65%+ AND your employer refuses to share any of their 15% NI saving — a genuinely bad combination that exists but is rarer than the SIPP-first crowd implies.

The fee gap matters most when your workplace default is the bottom decile and your employer is hostile to bonus salary sacrifice. Here are the conditions where I'd switch a contribution to a SIPP:

• Workplace default AMC above 0.65%: typically older Aegon or Scottish Widows schemes inherited from a 2010s employer. Check your scheme documents — the AMC is on page one of the annual statement.
• No global-tracker option in the workplace fund range: some schemes only offer UK-skewed lifestyle funds. If you're locked out of a Developed World or All-Cap tracker, you're paying for active mediocrity.
• Employer refuses to share any employer NI saving on sacrificed contributions: most do share, but check before assuming. If they keep all 15%, the NI maths still favours sacrifice but the margin narrows.
• You've hit the £60,000 annual allowance at work and need to use a previous-year carry-forward: a SIPP is the cleaner wrapper for catch-up contributions.
• You're a higher-rate taxpayer near £100,000 income with no salary-sacrifice scheme available: paying into a SIPP and claiming higher-rate relief is the only path to recovering the 60% marginal trap (where the personal allowance tapers off between £100,000 and £125,140 of adjusted income). See our pension tax relief guide for the full mechanics.

For everyone else — basic-rate PAYE, higher-rate with a normal scheme, anyone whose employer rebates any employer NI — sacrifice into the workplace pension up to the £60,000 annual allowance before you fund a SIPP.

The honest answer is rarely 'all SIPP' or 'all workplace'. It's salary-sacrifice the workplace pension to the limit of your employer's match, plus whatever sacrifice headroom you have, and then route any further pension saving into a SIPP for the wider fund choice. The SIPP becomes your overflow vehicle, not your primary one.

This routing also lets you consolidate old workplace pots from previous jobs into the SIPP (which is sensible if those old defaults are above 0.50% AMC), while leaving your current employer's contribution-match in the workplace scheme where it has to live.

The one thing you don't do is open a SIPP because the marketing made it sound like the smart-money default. The smart-money default is whichever wrapper compounds the most after-tax contribution into the most fund growth. For most PAYE employees in 2026, that's the workplace pension — for the boring reason that the National Insurance system rewards employer-routed pension saving more than it rewards individual SIPP saving.

For more on the salary-sacrifice mechanism, see our guide to the £40,000 bonus sacrifice. For the SIPP-vs-LISA flip on the same logic, see salary sacrifice at 32 beats the LISA. The full pensions hub covers annual-allowance rules and carry-forward.

This article is for informational purposes only and does not constitute financial advice. Pension and tax rules are complex and depend on individual circumstances. You should seek independent financial advice before making any pension or investment decisions.