ISA
Use the ISA allowance deliberately
If you meant to shelter cash or investments this tax year, March is the point where “I will do that later” becomes “that allowance is gone”.
Check the allowances that actually run out
Pension
Check whether pension top-ups are solving a real problem
For higher earners and families, a pension contribution can reduce ANI pain as well as increase long-term savings. Recheck the actual thresholds first.
Check the taxable-account drag before the year closes
CGT
Review realised gains, future sales and wrapper transfers
March is the right time to ask whether your taxable account decisions are still sensible, especially if you are holding appreciated shares or investment funds outside wrappers.
Income and distributions
Check what the account is forcing you to track
If your ETF choice or account structure is generating admin you do not actually want, that is useful information for next tax year as well.
Do the final threshold review before 5 April
ANI and family support
Recheck the household thresholds one last time
Child Benefit, Personal Allowance taper and childcare support can all hinge on numbers that look small relative to the total salary but matter a lot in practice.
Cashflow and admin
Make next year easier while this year is still open
If one part of the setup keeps creating friction, use this review to simplify the wrapper choice, payroll route or account structure for the year ahead.