{
  "id": "swp",
  "version": "4d26e5072cf8",
  "status": "published",
  "name": "SWP Calculator",
  "question": "How long will my SWP last?",
  "summary": "Computes what is left of an investment after fixed monthly withdrawals, how much you take out, the interest earned, and when the money runs out.",
  "category": "finance",
  "subcategory": "investing",
  "url": "https://www.acalculator.org/finance/swp-calculator",
  "markdown": "https://www.acalculator.org/finance/swp-calculator.md",
  "kind": "schedule",
  "method": "Each month, add interest at the yearly rate ÷ 12, then take out the withdrawal (or whatever is left, if that is less).",
  "assumptions": [
    "The return is a nominal yearly rate compounded monthly: each month earns the rate ÷ 12.",
    "Withdrawals come out at the end of each month, after that month’s interest.",
    "When the balance cannot cover a withdrawal, the last withdrawal is what is left and the plan stops.",
    "The return does not change. Tax, exit loads, and fees are not included."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "totalInvestment": {
        "title": "Amount invested",
        "description": "The lump sum invested at the start.",
        "type": "number",
        "x-unit": "USD",
        "exclusiveMinimum": 0,
        "maximum": 1000000000
      },
      "withdrawalAmount": {
        "title": "Take out each month",
        "description": "The fixed amount withdrawn at the end of every month.",
        "type": "number",
        "x-unit": "USD",
        "minimum": 0,
        "maximum": 100000000
      },
      "expectedReturn": {
        "title": "Expected return (per year)",
        "description": "The expected yearly return, as a nominal rate compounded monthly (the yearly rate divided by 12 each month).",
        "type": "number",
        "x-unit": "percent",
        "minimum": 0,
        "maximum": 50
      },
      "timePeriod": {
        "title": "For how long? (years)",
        "description": "How many years of withdrawals to plan for.",
        "type": "integer",
        "minimum": 1,
        "maximum": 60
      }
    }
  },
  "outputs": {
    "balance": {
      "label": "Left at the end",
      "description": "The balance after the last month of the plan, or 0 when the money runs out first.",
      "format": "money"
    },
    "takenOut": {
      "label": "Total taken out",
      "description": "All withdrawals added up.",
      "format": "money"
    },
    "interest": {
      "label": "Total interest earned",
      "description": "All the return earned: what is left plus what was taken out, minus the amount invested.",
      "format": "money"
    },
    "outcome": {
      "label": "What the plan does",
      "description": "In words: what is left after the years of the plan, or how long the withdrawals last when the money runs out first.",
      "format": "text"
    },
    "lasts": {
      "label": "The money runs out after",
      "description": "How long the withdrawals last when the money runs out before the end of the plan.",
      "format": "duration"
    },
    "sustainable": {
      "label": "Most you can take each month",
      "description": "The level monthly withdrawal that uses up the investment exactly at the end of the plan: the annuity payment for the amount invested.",
      "format": "money"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "totalInvestment": 100000,
      "withdrawalAmount": 1000,
      "expectedReturn": 8,
      "timePeriod": 10
    },
    "outputs": {
      "balance": 39017.98827276355,
      "takenOut": 120000,
      "interest": 59017.988272763556,
      "outcome": "leaves $39,017.99 after 10 years",
      "sustainable": 1213.2759435535695
    },
    "text": "Taking $1,000.00 a month from $100,000.00 at 8% a year leaves $39,017.99 after 10 years, after taking out $120,000.00."
  },
  "examples": [
    {
      "given": {
        "totalInvestment": 100000,
        "withdrawalAmount": 1000,
        "expectedReturn": 8,
        "timePeriod": 10
      },
      "expect": {
        "balance": 39017.98827276355,
        "takenOut": 120000,
        "interest": 59017.988272763556,
        "sustainable": 1213.2759435535777
      },
      "source": "future value of a sum less an annuity: 100,000 × (1 + 0.08/12)^120 − 1,000 × ((1 + 0.08/12)^120 − 1) ÷ (0.08/12); hand calculation in content.mdx; U.S. Securities and Exchange Commission, Investor.gov compound interest formula. https://www.investor.gov/financial-tools-calculators/calculators/compound-interest-calculator"
    },
    {
      "given": {
        "totalInvestment": 50000,
        "withdrawalAmount": 1500,
        "expectedReturn": 8,
        "timePeriod": 1
      },
      "expect": {
        "balance": 35475.08630868561,
        "interest": 3475.0863086856198,
        "takenOut": 18000
      },
      "source": "the same annuity formula over 12 months; hand calculation in content.mdx; U.S. Securities and Exchange Commission, Investor.gov compound interest formula. https://www.investor.gov/financial-tools-calculators/calculators/compound-interest-calculator"
    },
    {
      "given": {
        "totalInvestment": 100000,
        "withdrawalAmount": 2000,
        "expectedReturn": 6,
        "timePeriod": 10
      },
      "expect": {
        "balance": 0,
        "takenOut": 115361.35663493986,
        "lasts": {
          "years": 4,
          "months": 10
        }
      },
      "source": "month-by-month run of the rule in content.mdx; the 58th withdrawal is the part that is left; U.S. Securities and Exchange Commission, Investor.gov compound interest formula. https://www.investor.gov/financial-tools-calculators/calculators/compound-interest-calculator"
    },
    {
      "given": {
        "totalInvestment": 100000,
        "withdrawalAmount": 1000,
        "expectedReturn": 0,
        "timePeriod": 10
      },
      "expect": {
        "balance": 0,
        "takenOut": 100000,
        "interest": 0,
        "lasts": {
          "years": 8,
          "months": 4
        }
      },
      "source": "hand calculation in content.mdx: 100,000 ÷ 1,000 = 100 months at 0%; U.S. Securities and Exchange Commission, Investor.gov compound interest formula. https://www.investor.gov/financial-tools-calculators/calculators/compound-interest-calculator"
    }
  ],
  "sources": [
    "Future value of a sum less an annuity, and the annuity payment: S. A. Broverman, Mathematics of Investment and Credit, chapters 2 and 3.",
    "U.S. Securities and Exchange Commission, Investor.gov compound interest formula. https://www.investor.gov/financial-tools-calculators/calculators/compound-interest-calculator"
  ],
  "related": [
    "compound-interest",
    "rd"
  ],
  "changelog": [
    {
      "date": "2026-09-29",
      "note": "Worked examples name a published reference for their rule."
    },
    {
      "date": "2026-10-01",
      "note": "When the money runs out early, the answer says when (“runs out after 5 years, 2 months”) instead of “leaves $0.00 after 10 years”."
    }
  ]
}