What Is an Annuity? A Plain-English Guide to Steady Income Streams
Annuities sound complicated but the concept is simple: a series of equal payments over time. Here's how to think about and price them.
The word "annuity" made my eyes glaze over for years. Insurance salespeople seemed to love it; financial journalists seemed suspicious of it. When I finally sat down with the maths, I realised that an annuity is just a name for something we all encounter constantly — a series of regular, equal payments. Once you can calculate what that stream is worth, a whole range of financial decisions gets clearer.
The Basic Definition
An annuity is a series of equal cash payments made at regular intervals over a set time period.
That's it. Your rent payments form an annuity. Monthly pension income is an annuity. A car loan's monthly instalments are an annuity. The maths that values them is the same maths whether we're talking about insurance products, pensions, or home loans.
Two Key Quantities: Present Value and Future Value
You can look at an annuity from two directions:
Present value (PV) of an annuity — what is the right-now worth of a stream of future payments, discounted at a given rate? This is what you'd pay today to receive that stream.
Future value (FV) of an annuity — if you invest equal amounts at regular intervals at a given rate, how much will you accumulate by the end?
Present value formula (ordinary annuity)
PV = PMT × [1 − (1 + r)^−n] / r
Where:
- PMT = payment amount per period
- r = discount rate per period (annual rate ÷ periods per year)
- n = total number of payments
Future value formula (ordinary annuity)
FV = PMT × [(1 + r)^n − 1] / r
Ordinary Annuity vs Annuity Due
| Feature | Ordinary annuity | Annuity due |
|---|---|---|
| Payment timing | End of each period | Start of each period |
| Common examples | Mortgage, bond coupon | Rent, lease |
| Relative value | Lower | Higher (by factor of 1 + r) |
Because annuity-due payments arrive one period earlier, you can convert between the two:
PV (annuity due) = PV (ordinary annuity) × (1 + r)
Worked Example: Valuing a Payment Stream
You are offered a contract that pays $1,000 per month for 10 years (120 payments). The appropriate discount rate is 5% per year (0.4167% per month). What is this stream worth in today's money?
Using the ordinary annuity PV formula:
r = 0.05 / 12 = 0.004167
n = 120
PMT = $1,000
PV = $1,000 × [1 − (1 + 0.004167)^−120] / 0.004167
= $1,000 × [1 − (1.004167)^−120] / 0.004167
= $1,000 × [1 − 0.6070] / 0.004167
= $1,000 × 0.3930 / 0.004167
= $1,000 × 94.28
≈ $94,280
Even though you receive $120,000 in total ($1,000 × 120 months), the present value is only $94,280 — because future money is worth less than present money, and you're discounting at 5%. Use the annuity calculator to model your own scenario, or the present value calculator for a single-payment comparison.
When Annuities Make Sense
Retirement income
The core appeal of an annuity in retirement is longevity insurance — guaranteed income you cannot outlive. If you're worried about drawing down a portfolio over an unknown lifespan, an annuity removes that uncertainty (at a price: you typically get less than the actuarially fair value in exchange for the insurer bearing the risk).
Pension buyouts
Many defined-benefit pensions offer a lump-sum buyout option. To evaluate it, calculate the present value of your expected pension stream and compare it to the lump sum. If the lump sum is higher, consider taking it (especially if you're confident you can invest well). If lower, the pension stream may be worth more — but factor in the employer/fund's credit risk.
Structured settlements and lottery winnings
These are classic annuity-vs-lump-sum decisions. The present value calculation is your answer. The future value calculator can show what a lump sum would grow to if invested, giving you a fair comparison.
Fixed vs Variable Annuities
Fixed annuity: Payments are set at a predetermined amount. You know exactly what you'll receive. The risk: inflation erodes purchasing power over time, especially for very long annuity periods.
Variable annuity: Payments fluctuate with the performance of an underlying investment sub-account (often mutual funds). Upside potential, but also downside risk — payments may fall. Variable annuities typically carry higher fees than fixed ones.
Indexed annuity: A hybrid — returns are linked to a market index (like the S&P 500) but with a floor that prevents negative returns. The trade-off: upside is capped. Complexity is high.
For most people approaching retirement, the simplest approach is still a diversified portfolio with a systematic withdrawal plan — see how much do I need to retire? and what is the FIRE movement? for the framework — potentially supplemented with a small annuity for a baseline income floor.
The Retirement Calculator as a Complement
An annuity guarantees a payment stream; a portfolio gives flexibility. Most financial planners recommend a mix. The retirement calculator helps you model how long a portfolio lasts at a given withdrawal rate, while the annuity calculator helps you price the guaranteed-income alternative.
Key Takeaways
- An annuity is any series of equal, regular payments; its present value = PMT × [1 − (1 + r)^−n] / r.
- A $1,000/month payment stream for 10 years at 5% discount rate is worth approximately $94,280 today — not $120,000, because future money is worth less.
- Annuities are useful for retirement income certainty but transfer upside potential to the insurer; compare the present value of the payment stream against any lump-sum alternative before deciding.
All figures are illustrative. Past returns don't guarantee future results. Consider speaking with a financial advisor before making investment decisions.
Frequently asked questions
What is an annuity?+
An annuity is a financial product or arrangement that delivers a series of equal payments at regular intervals over a defined period — or for life. In finance, "annuity" also refers to any such stream of payments, which can be valued using present-value mathematics.
What is the difference between an ordinary annuity and an annuity due?+
In an ordinary annuity (also called annuity-in-arrears), payments occur at the end of each period — a typical mortgage or bond coupon. In an annuity due, payments occur at the start of each period — a common structure for lease or rent payments. An annuity due is always worth slightly more than an equivalent ordinary annuity because each payment arrives one period earlier.
What is the difference between a fixed and variable annuity?+
A fixed annuity pays a guaranteed amount per period regardless of market conditions — predictable and safe, but potentially eroded by inflation. A variable annuity ties payments to the performance of underlying investments, offering upside potential but also risk that payments may fluctuate or decline.
How do I know if a pension lump-sum buyout is worth taking?+
Calculate the present value of all future pension payments you would receive if you stayed in the scheme (using a realistic discount rate). Compare that to the lump sum offered. If the lump sum exceeds the present value, the buyout may be financially favourable. If it is lower, the pension stream is worth more — assuming the pension provider remains solvent. Use the annuity calculator to run this comparison.
Can I build my own annuity instead of buying one?+
In principle, yes — a diversified portfolio with a systematic withdrawal plan (like the 4% rule discussed in FIRE planning) mimics an annuity. The trade-off: you retain control and potential upside, but you bear longevity risk (the risk of outliving your money). A commercial annuity transfers that risk to an insurer in exchange for a premium baked into lower payments.
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Keep reading
- How Much Do I Need to Retire?
Your retirement number isn't a mystery — it starts from one figure (your annual spending) and the 25x rule turns it into a target you can actually plan toward.
- What Is the FIRE Movement? Financial Independence, Retire Early Explained
FIRE isn't about hating your job — it's about buying yourself choices. Here's the math behind Financial Independence, Retire Early.
- What Is a Good Rate of Return on Investments?
A "good" return depends on how you measure it and what you subtract — and the only number that truly matters is what's left after inflation.
Priya is a long-term investing nerd who loves a good spreadsheet. She writes the kind of guides she wishes she’d had when she started saving in her twenties.