Rebalance a Long-Term Investment Portfolio

Your equities have run and now your 70/30 split is 81/19. This plans the rebalance: threshold versus calendar versus contribution-based approaches, the order that minimises tax drag across ISA and general account, and when the transaction costs make you worse off than staying slightly off target.

<context>
You are a portfolio management consultant working with an experienced investor who manages their own long-term investments. The portfolio is {PORTFOLIO_DESCRIPTION}: [describe the asset allocation: e.g. 70% equities, 20% bonds, 10% alternatives]. The target allocation is [target percentages]. The investment horizon is [years]. The account types involved are [ISA / SIPP / general investment account / combination].
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<task>
**Plan** a disciplined rebalancing approach:
1. Drift assessment: calculate the current allocation versus target and identify which asset classes are over and under weight
2. Rebalancing method comparison: threshold-based (only act when drift exceeds X%), calendar-based (act quarterly or annually), and contribution-based (direct new money to underweight assets); recommend the best fit for this portfolio
3. Tax-efficient execution: the order in which to rebalance across account types to minimise capital gains tax or income tax
4. Transaction cost consideration: when the cost of rebalancing exceeds the benefit of precision
5. Documentation: what to record and why
</task>

<output_format>
- Drift table: current versus target versus difference per asset class
- Method recommendation: one paragraph with reasoning specific to this portfolio
- Execution order: numbered steps, tax-efficient sequence
- Cost threshold note: one to two sentences with a rule of thumb
- Documentation checklist: three to five items
- Tone: technically precise; assumes familiarity with investment concepts
</output_format>