The Seraph blog

Retirement, run through the numbers.

Each post builds a specific household, runs it through the Monte Carlo engine that powers the app, and reports the results.

SEPTEMBER 17, 2026 INTEREST RATES LIFETIME INCOME

How higher interest rates affect annuity pricing

Corporate bond yields rose about a percentage point over the past year, and the Federal Reserve added to it last week. We price the effect on annuity income at every age from 60 to 80, then work through who partial annuitization suits and who it does not.

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SEPTEMBER 1, 2026 DYNAMIC SPENDING STRATEGY

Spending guardrails in retirement planning and how they help

Cutting spending in downturns reliably lifts a plan's success rate, and the cuts themselves are worth measuring too. We ran one retiree's plan at eleven cut allowances from 0 to 50 percent: success climbs from 68 to 84 percent and levels off, while the average lifetime spending cut grows to $124,000.

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AUGUST 16, 2026 RULES OF THUMB WITHDRAWAL RATES

Is the 4 percent rule safe? We graded it twenty times.

Bengen now says 4.7 percent, Morningstar says 3.9. Run for three retirees at 50, 65, and 75 and rates from 3 to 6 percent, the same rule succeeds anywhere from 24 to 96 percent of the time, and the same million lands at 76 or 62 depending on which account holds it.

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AUGUST 9, 2026 CURRENT EVENTS SOCIAL SECURITY

Social Security runs short in 2032. What does a 22 percent cut do to your plan?

The trustees put the retirement fund's depletion in late 2032, with 78 percent of benefits payable after. Run across 2,000 lifetimes at claim ages 62, 67, and 70, the cut flips the claiming decision.

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AUGUST 2, 2026 CURRENT EVENTS CAREER RISK

What is AI going to do to my retirement?

A layoff at 57 takes this household's plan from 89 to 24 percent. Each repair priced across 5,000 simulated lifetimes, plus an AI-economy scenario.

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JULY 29, 2026 UNDER THE HOOD ENGINEERING

How do you port a financial model and know you didn't break it?

A retirement planner that is wrong does not crash; it returns a plausible number. The correctness infrastructure that keeps the engine reproducing its reference implementation to the cent: an exact-match oracle, a decoupling discipline, and a frozen seed schedule.

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JULY 26, 2026 EARLY RETIREMENT HEALTH INSURANCE

Retiring at 55 with $1.2 million? Watch the tightrope at $62,600.

From 55 to 65 your income sets your health insurance premium. SEPP sizing, the subsidy cliff, and Roth conversion timing, run across 5,000 lifetimes per strategy.

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JULY 19, 2026 SOCIAL SECURITY

Taking Social Security at 62 or 70? Let's actually run it.

The rule of thumb says wait for the bigger check. Across 2,000 simulated lifetimes the two paths come out even, and the deciding factor is a health insurance subsidy the early claimer unlocks.

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