Follow-up: comparison of UK take-home calculators (pension + student loan handling)

InspectahDave

A couple of weeks ago I asked about simplicity vs completeness in take-home calculators and received some helpful pushback — particularly around pension mechanisms and student loans.

I took a step back and benchmarked some of the web-based calculators mentioned for 2025/26 to see how consistently they implement:

• NET pay vs relief at source vs salary sacrifice
• Student loan plans
• Tax code handling
• Scottish rates
• Employer pension contributions
• Transparency of assumptions

For straightforward PAYE cases, most calculators align closely.

Where divergence appears is pension modelling — specifically how the mechanism is implemented and labelled.

I looked at four different scenarios and in one higher-income salary case (£135k gross, £20k sacrifice, Plan 2 loan), income tax aligned across tools that support salary sacrifice, but NI and student loan figures differed depending on how gross pay was reduced before thresholds were applied.

In other cases, the divergence wasn’t arithmetic error but:

• Pension mechanisms not clearly documented
• Salary sacrifice not supported
• Tax codes accepted without validation
• Student loan plan coverage varying

None of the calculators reviewed support capital gains modelling.

I’m not suggesting existing tools are unusable — most work well for straightforward cases — but the implementation details around pensions do make a difference in more complex scenarios.

Here are the specific income scenarios that I ran if anyone is interested.

DRS1

Have you seen this thread?

Self Assessment / pension / tax calculating - Page 4 — MoneySavingExpert Forum

InspectahDave

https://forums.moneysavingexpert.com/discussion/comment/81909268#Comment_81909268

Thanks for the link — that looks like it’s touching on exactly the same issue around pension treatment and how calculators model it. I’ll have a read through that thread as well.