Why September is a good time for a tax-year check-in

by Julie Harris - Technical Lead - Oak Four - September 2026

Most people associate tax planning with March.

The tax year is almost over, deadlines are approaching and suddenly there is a flurry of activity around ISAs, pensions and other allowances.

But from a planning perspective, September can be a much more useful time to look at things.

We still have more than six months before the tax year ends on 5 April.

Which means there is time to plan rather than simply react.

Not all allowances work in the same way

One of the complications of the UK tax system is that different allowances have different rules.

Take ISAs.

For the current 2026/27 tax year, an individual can subscribe up to £20,000 into ISAs. But unused ISA allowance cannot simply be carried into the following tax year.

Pensions are different.

The standard pension annual allowance is currently £60,000, although the amount available can be lower for some people, including those with higher incomes or those who have flexibly accessed pension benefits. Subject to the rules, unused annual allowance from the previous three tax years can sometimes be carried forward.

Capital Gains Tax has another set of rules again.

The annual exempt amount for an individual is currently £3,000. Unlike pension carry forward, an unused CGT annual exemption is lost at the end of the tax year.

And for estate planning, the annual Inheritance Tax gifting exemption is also £3,000, although unused exemption can be carried forward for one tax year only.

Same tax year.

Four allowances.

Four different sets of considerations.

This is one reason financial planning is about much more than remembering a list of limits.

The numbers need to fit the plan

Just because an allowance exists does not automatically mean it should be used.

Putting more into a pension may be tax-efficient, for example, but that money also needs to fit with your wider requirements for accessibility, income and future spending.

Likewise, realising an investment gain simply to use a Capital Gains Tax exemption may not make sense if it conflicts with the investment strategy.

And making gifts for estate-planning purposes should begin with a much more important question:

Can you comfortably afford to give the money away?

Tax should influence good financial planning.

It shouldn't dictate it.

Why we look ahead

A significant part of the technical planning work we do at Oak Four happens away from the meeting room.

We keep track of contributions already made.

We look at allowances that may still be available.

We consider previous pension input where carry forward might be relevant.

We review gains and losses.

And, importantly, we look at all of this alongside your cashflow plan and the things you actually want your money to achieve.

Sometimes that means taking action.

Sometimes it means deliberately doing nothing.

Both can be good planning decisions.

March is better without surprises

There will always be some things that cannot be known until later in the tax year.

Income may change. Bonuses may be paid. Investments may move in value. Personal circumstances can change.

But the earlier we identify the decisions that are likely to matter, the more options we tend to have.

That is why we don't think tax-year planning should begin in March.

By then, we ideally want to be implementing a plan we've already been thinking about for several months.

Because good tax planning isn't really about rushing to use every allowance before midnight on 5 April.

It's about making sensible decisions, at the right time, as part of a much bigger financial plan.