{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"savings-withdrawal"},"result":{"entity_type":"calculator","id":"savings-withdrawal","calculator_id":"savings-withdrawal","canonical_url":"https://tttkmbb.com/finance/savings-withdrawal","name":"Savings Withdrawal Calculator","title":"Savings Withdrawal Calculator – How Long a Balance Lasts, or the Sustainable Monthly Withdrawal","category":"finance","category_name":"Finance","tool_name":"calculate_savings_withdrawal","featured_mcp_tool":false,"description":"Given a balance earning a monthly-compounded return, computes how many months a fixed monthly withdrawal lasts (and the total withdrawn and interest earned), or the level monthly withdrawal that exhausts the balance over a chosen number of years, plus the interest-only withdrawal that preserves the balance forever.","use_when":"You are drawing down savings, a retirement account or an inheritance and want either the depletion date for a given withdrawal or the affordable withdrawal for a given period.","do_not_use_when":"You want the required portfolio for a withdrawal rate (use fire-number) or are still accumulating (use retirement-savings or compound-interest).","inputs":[{"name":"balance","label":"Starting balance","type":"number","required":true,"max":1000000000000,"exclusive_min":0,"description":"Amount available at the start.","example":500000},{"name":"annual_return_percent","label":"Annual return","type":"number","unit":"%","required":true,"min":0,"max":50,"description":"Nominal annual return in percent, compounded monthly.","example":5},{"name":"monthly_withdrawal","label":"Monthly withdrawal","type":"number","required":false,"max":1000000000,"exclusive_min":0,"description":"Fixed amount withdrawn at the end of every month; enables the how-long-it-lasts result.","example":3000},{"name":"years","label":"Years the money should last","type":"number","unit":"years","required":false,"max":100,"exclusive_min":0,"description":"Enables the sustainable monthly withdrawal that empties the balance after exactly this many years.","example":20}],"outputs":[{"name":"perpetual_monthly_withdrawal","label":"Interest-only withdrawal","type":"number","decimals":2,"description":"balance × annual_return_percent / 1200: taking only this each month never touches the principal."},{"name":"months_lasting","label":"Months the balance lasts","type":"integer","unit":"months","decimals":0,"description":"Number of monthly withdrawals until the balance is exhausted (includes the smaller final one); only for monthly_withdrawal."},{"name":"duration","label":"Duration","type":"string","decimals":4,"description":"months_lasting in years and months, or 'indefinitely' when the withdrawal does not exceed monthly interest."},{"name":"total_withdrawn","label":"Total withdrawn","type":"number","decimals":2,"description":"Sum of all withdrawals until depletion."},{"name":"total_interest_earned","label":"Interest earned during drawdown","type":"number","decimals":2,"description":"total_withdrawn − balance."},{"name":"final_withdrawal","label":"Final withdrawal","type":"number","decimals":2,"description":"The last, usually smaller, withdrawal that empties the account."},{"name":"sustainable_monthly_withdrawal","label":"Sustainable monthly withdrawal","type":"number","decimals":2,"description":"Level withdrawal that exhausts the balance after exactly `years` (only when years is given)."},{"name":"sustainable_total_withdrawn","label":"Total withdrawn over the period","type":"number","decimals":2,"description":"sustainable_monthly_withdrawal × 12 × years."}],"input_schema":{"type":"object","properties":{"balance":{"description":"Amount available at the start.","type":"number","maximum":1000000000000,"exclusiveMinimum":0,"examples":[500000]},"annual_return_percent":{"description":"Nominal annual return in percent, compounded monthly. Unit: %.","type":"number","minimum":0,"maximum":50,"examples":[5],"x-unit":"%"},"monthly_withdrawal":{"description":"Fixed amount withdrawn at the end of every month; enables the how-long-it-lasts result.","type":"number","maximum":1000000000,"exclusiveMinimum":0,"examples":[3000]},"years":{"description":"Enables the sustainable monthly withdrawal that empties the balance after exactly this many years. Unit: years.","type":"number","maximum":100,"exclusiveMinimum":0,"examples":[20],"x-unit":"years"}},"additionalProperties":false,"required":["balance","annual_return_percent"]},"output_schema":{"type":"object","properties":{"perpetual_monthly_withdrawal":{"description":"balance × annual_return_percent / 1200: taking only this each month never touches the principal.","type":"number"},"months_lasting":{"description":"Number of monthly withdrawals until the balance is exhausted (includes the smaller final one); only for monthly_withdrawal. Unit: months.","type":"integer","x-unit":"months"},"duration":{"description":"months_lasting in years and months, or 'indefinitely' when the withdrawal does not exceed monthly interest.","type":"string"},"total_withdrawn":{"description":"Sum of all withdrawals until depletion.","type":"number"},"total_interest_earned":{"description":"total_withdrawn − balance.","type":"number"},"final_withdrawal":{"description":"The last, usually smaller, withdrawal that empties the account.","type":"number"},"sustainable_monthly_withdrawal":{"description":"Level withdrawal that exhausts the balance after exactly `years` (only when years is given).","type":"number"},"sustainable_total_withdrawn":{"description":"sustainable_monthly_withdrawal × 12 × years.","type":"number"}}},"formula":"i = annual_return_percent/1200. Duration: months = −ln(1 − i × balance / monthly_withdrawal) / ln(1 + i), rounded up (balance / withdrawal if i = 0); no finite duration if monthly_withdrawal ≤ balance × i. Sustainable withdrawal over n = 12 × years months: W = balance × i / (1 − (1 + i)^−n).","method":"Ordinary-annuity arithmetic: interest is credited monthly on the remaining balance and withdrawals are taken at month end (the same formula as a loan payment with the roles reversed). Returns are assumed constant; inflation and taxes are ignored.","sources":[{"name":"Wikipedia – Amortization calculator (annuity payment formula)","url":"https://en.wikipedia.org/wiki/Amortization_calculator","type":"reference","retrieved_at":"2026-09-24"},{"name":"Wikipedia – Annuity","url":"https://en.wikipedia.org/wiki/Annuity","type":"reference","retrieved_at":"2026-09-24"},{"name":"Wikipedia – Trinity study (safe withdrawal rates)","url":"https://en.wikipedia.org/wiki/Trinity_study","type":"reference","retrieved_at":"2026-09-24"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"500,000 at 5 %, withdraw 3,000 per month","inputs":{"balance":500000,"annual_return_percent":5,"monthly_withdrawal":3000},"expected":{"perpetual_monthly_withdrawal":2083.33,"months_lasting":286,"duration":"23 years 10 months","total_withdrawn":855427,"total_interest_earned":355427,"final_withdrawal":427},"url":"https://tttkmbb.com/api/v1/calculate/savings-withdrawal?balance=500000&annual_return_percent=5&monthly_withdrawal=3000"},{"name":"300,000 at 4 % to last 20 years","inputs":{"balance":300000,"annual_return_percent":4,"years":20},"expected":{"perpetual_monthly_withdrawal":1000,"sustainable_monthly_withdrawal":1817.94,"sustainable_total_withdrawn":436305.84},"url":"https://tttkmbb.com/api/v1/calculate/savings-withdrawal?balance=300000&annual_return_percent=4&years=20"}],"faq":[{"q":"Why does the money last so long at 5 %?","a":"Interest on 500,000 at 5 % is about 2,083 per month, so a 3,000 withdrawal only draws the principal down by about 917 at first; the drawdown accelerates as the balance and its interest shrink."},{"q":"Should I use a real or nominal return?","a":"If the withdrawal should keep its purchasing power, enter a real return (nominal minus inflation) and treat the withdrawal as today's money; otherwise the fixed nominal withdrawal buys less each year."}],"tags":["savings withdrawal","how long will my money last","drawdown calculator","retirement withdrawal","annuity withdrawal","sustainable withdrawal"],"related":[{"calculator_id":"fire-number","reason":"Portfolio needed for a chosen withdrawal rate."},{"calculator_id":"retirement-savings","reason":"Grow the balance before drawing it down."},{"calculator_id":"loan-payment","reason":"The same annuity formula applied to a loan."}],"links":{"html":"https://tttkmbb.com/finance/savings-withdrawal","markdown":"https://tttkmbb.com/finance/savings-withdrawal.md","json":"https://tttkmbb.com/finance/savings-withdrawal.json","api":"https://tttkmbb.com/api/v1/calculate/savings-withdrawal","schema":"https://tttkmbb.com/api/v1/calculators/savings-withdrawal","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T02:02:08Z"}