SWP Calculator

Created by Arunangshu DasReviewed Nov 10, 2026

Model fixed monthly withdrawals from an opening balance and see when the portfolio falls short.

Compare beginning and end of month withdrawal timing and separate requested, paid and unmet amounts.

Projected ending balance

Enter a withdrawal plan or load the worked example.

Month numbers start at 1 for both timings. A payment cannot exceed the available balance. Growth uses equal model months and a constant assumed return.

Understand what drives the projection

Walk through withdrawal order, partial payments and exact depletion.

Read the complete SWP guide

Formula and methodology

Ending balance = opening balance + signed growth − paid withdrawals.

Convert the effective annual decimal return A to monthly factor f = (1 + A)^(1/12). At beginning timing, pay up to the opening monthly balance and multiply what remains by f. At end timing, multiply the balance by f first and then pay up to that grown balance.

Definitions

A systematic withdrawal plan (SWP) takes regular amounts from an invested balance. This model uses one opening balance and one fixed request per complete model month.

Verified worked examples

Start with 1,000, request 400 a month for three months and assume zero return. The payments are 400, 400 and 200. Requested withdrawals total 1,200, paid withdrawals total 1,000 and unmet withdrawals total 200. Depletion and first shortfall both occur in month 3.

Interpretation

Opening balance plus signed modeled growth less paid withdrawals equals ending balance. Requested less paid equals unmet. A full payment can deplete the portfolio exactly, so a shortfall might only appear in a later month.

Inputs and interpretation

Enter opening balance, fixed monthly withdrawal request, effective annual percentage and whole months. Choose beginning or end timing. Read the ending balance, withdrawal totals and first-shortfall payment together.

Assumptions and limitations

Each month is an equal period. Both timing options label the first request month 1. If a request exceeds available funds, pay the available balance. Zero horizon makes no requests, and an opening zero balance is already empty.

Supported domain and common mistakes

Enter 0 through 10^12 for both monetary inputs, 0 through 1,200 months and an effective annual percentage above −100% and at most 100%. Inputs allow 12 fractional digits. Arithmetic uses at least 100 significant digits, flags unresolved thresholds and rejects ending balances above 10^30.

Keep requested amounts separate from actual modeled payments and growth. A positive ending balance in this scenario does not establish a safe withdrawal amount.

Frequently asked questions

How does an SWP calculator work?

It applies a constant monthly growth factor to a balance and pays each monthly request up to the amount available at the selected checkpoint.

Can the last payment be smaller than the request?

Yes. The model pays the available amount, reports the rest as unmet, and leaves a zero balance.

What is the difference between depletion and first shortfall?

Depletion is the month a positive portfolio reaches zero. An exactly funded last payment can deplete the balance before any request goes unpaid.

How is the monthly rate calculated?

Take the twelfth root of one plus the effective annual rate as a decimal and subtract one. For 12% effective annual return the monthly rate is about 0.948879%.

What happens at zero months?

There are no requests or payments. The ending balance equals the opening balance and growth is zero.

Can I use a negative return?

Yes, above −100%. A negative rate reduces positive balances exposed to the modeled monthly growth period.

Sources and educational scope

Educational constant-return model. It excludes dates, real market paths, fees, taxes, inflation, FX and product or account rules. It does not guarantee income or provide personalized investment advice.

Reviewed 2026-11-10. AI-assisted content under operator editorial responsibility. No independent expert financial review is claimed.