happytails.ai

Savings withdrawal calculator

Open Savings withdrawal calculator on Happytails.ai. This view has the same page content and links, with explicit tool capabilities. Read the processing notes before using a tool.

Tool capabilities

{
  "id": "savings-withdrawal-calculator",
  "category": "finance-tools",
  "built": true,
  "requirements": "Starting balances, withdrawals and target balances up to 1000000000000 at 0 to 3 decimal places, 100000000000 at 4, 10000000000 at 5 and 1000000000 at 6, with every month-end balance within 1000000000000000 minor currency units (10000000000000 at 2 decimal places), rates from 0 to 100 percent, 1 to 1200 months and yearly increases from 0 to 100 percent. Calculated locally in your browser. Downloads are a JSON report and a CSV with one row per month.",
  "implementation": {
    "fields": [
      {
        "key": "opening",
        "label": "Starting balance",
        "value": "200000",
        "type": "text",
        "maxLength": 30,
        "help": "The balance before the first withdrawal."
      },
      {
        "key": "rate",
        "label": "Yearly interest or return (%)",
        "value": "4",
        "type": "text",
        "maxLength": 20,
        "help": "From 0 to 100, the same every month."
      },
      {
        "key": "months",
        "label": "Months to model",
        "value": "300",
        "type": "text",
        "maxLength": 10,
        "help": "Whole months from 1 to 1200."
      },
      {
        "key": "mode",
        "label": "Calculate",
        "value": "depletion",
        "type": "select",
        "values": [
          "depletion",
          "sustainable"
        ],
        "labels": {
          "depletion": "How long a withdrawal lasts",
          "sustainable": "The largest withdrawal that lasts"
        }
      },
      {
        "key": "withdrawal",
        "label": "Monthly withdrawal",
        "value": "1200",
        "type": "text",
        "maxLength": 30,
        "help": "Taken each month until the balance runs out.",
        "showWhen": {
          "mode": [
            "depletion"
          ]
        }
      },
      {
        "key": "target",
        "label": "Balance to keep at the end",
        "value": "0",
        "type": "text",
        "maxLength": 30,
        "help": "The sustainable withdrawal leaves at least this amount. Enter 0 to use the whole balance.",
        "showWhen": {
          "mode": [
            "sustainable"
          ]
        }
      },
      {
        "key": "timing",
        "label": "Withdrawal timing",
        "value": "start",
        "type": "select",
        "values": [
          "start",
          "end"
        ],
        "labels": {
          "start": "Start of each month",
          "end": "End of each month"
        }
      },
      {
        "key": "credit",
        "label": "Interest credited",
        "value": "monthly",
        "type": "select",
        "values": [
          "monthly",
          "quarterly",
          "semiannual",
          "annual"
        ],
        "labels": {
          "monthly": "Monthly",
          "quarterly": "Quarterly",
          "semiannual": "Every 6 months",
          "annual": "Yearly"
        }
      },
      {
        "key": "increase",
        "label": "Yearly withdrawal increase (%)",
        "value": "0",
        "type": "text",
        "maxLength": 20,
        "help": "From 0 to 100, applied every 12 months."
      },
      {
        "key": "decimals",
        "label": "Decimal places in amounts",
        "value": "2",
        "type": "select",
        "values": [
          "2",
          "0",
          "1",
          "3",
          "4",
          "5",
          "6"
        ]
      }
    ],
    "registrationFamily": "personal-balance-schedules",
    "input": false,
    "note": "Calculated on your device over at most 1200 months.",
    "experience": {
      "automatic": false,
      "single": false,
      "inputMaxLength": 1000000,
      "inputMode": "text",
      "label": "Balance and withdrawal values",
      "placeholder": "Enter values in the form fields",
      "help": "This calculator reads the form fields below; there is no text box. Up to 1,000,000 characters. Review the settings before running.",
      "helpParts": [
        "This calculator reads the form fields below; there is no text box.",
        "Up to 1,000,000 characters.",
        "Review the settings before running."
      ],
      "action": null
    },
    "mode": "explicit",
    "interactive": false
  },
  "execution": "Browser interface",
  "api": null,
  "browser_agent": {
    "supported": true,
    "name": "run_current_tool",
    "discovery": "WebMCP on the human page in a supporting browser",
    "verification": "See audit/API-AUDIT.md; availability is not verification"
  }
}

Page guide

See how long a savings balance lasts with monthly withdrawals, or find the largest monthly withdrawal that lasts for the months you choose. Interest, yearly increases and the month the money runs out are shown in a full schedule.

How to use Savings withdrawal calculator
  1. Enter the starting balance, the yearly interest or return and the number of months.
  2. Choose whether to test a withdrawal or find the largest one that lasts.
  3. Enter the monthly withdrawal, or the balance you want to keep at the end.
  4. Choose the withdrawal timing, how often interest is credited and any yearly increase, then review and download the JSON report or the monthly CSV.

Useful next steps

Savings goalCompound interestSimple interest calculator

Method

The balance runs month by month. Interest accrues on the balance at the yearly rate divided by 12, rounded to the cent, and is credited at the end of each credit period. Withdrawals come out at the start or end of each month and rise every 12 months by your yearly increase. A withdrawal that would empty the account first receives the interest accrued so far; if it still cannot be paid in full, the account is depleted that month and the shortfall is shown.

Sustainable withdrawal

In the second mode the tool searches whole cents for the largest first-year withdrawal that is paid in full every month and leaves at least your target balance. It is the exact ledger version of the annuity relation behind the spreadsheet PV and PMT functions (Microsoft Support, PV function, checked 16 October 2026); one cent more falls short.

Assumptions and limits

The same return is applied every month. Real returns vary, and the order of good and bad years can change the outcome. Taxes, inflation and fees are not included. This is a calculation from your own numbers, not financial or retirement advice.