Personal-finance life decision math: loan prepayment vs SIP, and SWP vs FD (calc)

[iamsaquib8]

What

Roadmap idea. Every investor faces real-world personal finance crossroads that standard investment tools ignore:

• "Should I prepay my 8.5% home loan, or invest that money into an equity SIP?"
• "Should I switch my old Regular mutual funds to Direct plans, or will the capital gains tax wipe out the fee savings?"
• "Should retirees generate income via an SWP from an equity-savings fund, or stick with Fixed Deposits (FDs)?"

These decisions require exact, post-tax, post-fee compounding math tailored to Indian and global tax regimes.

Design

• stockwise calc prepay --loan-rate 8.5 --balance 35L --tenure 15 --sip-expected 12:
  • Compares the guaranteed post-tax interest saved by prepayment against the probabilistic return distribution of an equity SIP over the loan horizon (e.g. median, 10th percentile, 90th percentile post-12.5% LTCG).
  • Shows breakeven equity return required to beat prepayment.
• stockwise calc switch-direct <MF_CODE> [--units N]:
  • Computes the upfront STCG/LTCG tax payable today if switching from Regular to Direct.
  • Compares against the compounded TER difference (~0.5%–1.2% per year) over 3, 5, 10, and 15 years to calculate the exact breakeven holding period in months.
• stockwise calc swp-vs-fd --capital 50L --monthly 35000 --years 15:
  • Models post-tax monthly cash flows from bank FDs (taxed at investor's slab rate) vs Systematic Withdrawal Plans (SWP) from debt/hybrid/equity funds (taxed under respective LTCG rules).
  • Displays remaining corpus trajectory and probability of exhaustion.

Done when

• Exact post-tax formulas implemented with Indian tax brackets, cess, and capital gains rules.
• Breakeven horizons and probability ranges calculated deterministically.
• Clear disclaimer: mathematical projection, not financial planning advice.
• Exposes --json and MCP tool.

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Upvote or comment below with what life math questions you find hardest to calculate. Ideas with community demand get scheduled on the roadmap.