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Step-up SIP Calculator

Work out what a monthly investment grows into when you raise it each year with pay rises, compared with keeping the amount flat.

Your plan
£
%
%
yrs
£
Projected outcome
Value after 20 years 0
Total invested—
Growth on top—
Final monthly amount—
If you never stepped up—
Gained by stepping up—
Step-up vs flat contributions
Stepping up Flat amount Invested

A SIP (systematic investment plan) is simply investing a fixed amount every month. A step-up SIP raises that amount once a year — typically in line with a pay rise — so your investing grows with your income instead of standing still. Because the increases compound alongside the returns, a modest yearly step-up usually beats a large one-off increase later. The step-up is applied on each anniversary. Returns are assumed steady; see the Invest tab for a simulation showing the realistic spread of outcomes.

How the maths works

The formula behind this calculator, with a worked example built from your own inputs.

Step-up SIPStep-up SIP
Vₘ = Vₘ₋₁ × (1 + r) + cₘ   where   cₘ increases by s% every 12 months

r = monthly return  ·  c = the current monthly contribution  ·  s = yearly step-up.
There is no neat closed form because the contribution changes each year, so the tool steps month by month and raises the contribution on each anniversary. The comparison line simply runs the same maths with s = 0.

Worked example: £300/month, stepping up 10% a year at 8% return over 20 years grows to far more than the same £300 held flat — because each rise compounds for the remaining years.
About the currency selectorCurrency

Changing the currency relabels the figures — it does not convert them. There are no exchange rates involved, and nothing is fetched from the internet.

If you enter 280,000 and switch from pounds to dollars, the tool reads it as 280,000 dollars, not as a converted amount. The maths is identical in every currency because percentages, ratios and time don't care about the unit — a 25-year loan at 4.8% has the same payment-to-principal relationship whether it's in yen or rand.

What does change is formatting, which follows each region's own conventions: where the symbol sits (€ goes after the number in German), which separators are used (Switzerland uses apostrophes, South Africa uses spaces), how digits are grouped (India groups in lakhs — 1,71,120 rather than 171,120), and whether decimals exist at all (yen and won have no minor unit).

So pick the currency you're actually working in and enter local amounts. Don't enter pounds and switch to dollars expecting a conversion.

Assumptions & what these formulas ignoreImportant

Interest compounds monthly on the outstanding balance — standard for UK repayment mortgages, though some lenders calculate daily, giving slightly different totals.

Rates are assumed fixed for the whole term. In reality a fixed period ends and you revert or remortgage, so long-term totals are illustrative.

Not included anywhere: arrangement and broker fees, stamp duty, early repayment charges, void periods, maintenance, letting agent fees, income or capital gains tax, and inflation. Figures are in today's money.

Overpayment caps: many fixed deals limit penalty-free overpayments to around 10% of the balance a year.

Investment returns assume future variability resembles the past — which markets regularly break. Depreciation curves are typical patterns, not valuations; real resale depends on mileage, condition, spec and demand.

These tools are for estimating and comparing options. They aren't financial advice, and for a decision that matters it's worth speaking to a qualified adviser or broker.

Frequently asked questions

Direct answers about this calculator.

What is a step-up SIP and is it better than a regular SIP?

A SIP, or systematic investment plan, means investing a fixed amount every month. A step-up SIP increases that amount once a year, usually in line with a pay rise, so your investing grows with your income rather than standing still. Because each increase compounds for all the remaining years, a modest annual step-up generally beats a single larger increase made later. Investing 300 a month with a 10% annual step-up at an 8% return grows substantially more over 20 years than the same 300 held flat, and the monthly amount reaches about 1,835 by the final year.

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About these calculators

How the numbers are produced, what they are not, and where to get regulated advice.

How the numbers are produced

Every figure comes from a published formula shown openly in the How the maths works section, alongside a worked example built from your own inputs. Nothing is estimated, weighted or adjusted behind the scenes.

The calculations run entirely in your browser. Nothing is stored, no accounts, no tracking, no adverts, and no affiliate links to mortgage or insurance products. Nobody pays to appear here, so there is no incentive to nudge a result in any direction. The one time anything leaves your device is if you click Update to latest figures on the inflation tab — that makes a single request to the World Bank's open data API for newer price indices, and sends nothing about you. Every other figure, including the bundled inflation history, is already in the page.

Default rates and depreciation curves are typical illustrative figures, not live market data. The tools do not fetch interest rates, house prices, exchange rates or resale values from anywhere.

Limitations — read before relying on this

These are estimating tools for comparing options, not a substitute for professional advice. In particular:

· Figures exclude fees, stamp duty, early repayment charges, tax, void periods, maintenance and inflation.
· Rates are assumed fixed for the whole term; in reality fixed periods end and you revert or remortgage.
· Investment simulations assume future variability resembles the past — which markets regularly break. They show modelled uncertainty, not a forecast.
· Depreciation curves are typical patterns, not valuations. Real resale depends on mileage, condition, spec and demand.
· Changing currency relabels figures; it does not convert them.

For a decision that matters, speak to a qualified mortgage broker, accountant or FCA-regulated financial adviser. Nothing here is financial advice.

Sources & further reading

For impartial, regulated guidance in the UK:
· MoneyHelper — the government-backed free money guidance service
· MoneySavingExpert — mortgage guides and comparison tools
· Bank of England — current Bank Rate
· GOV.UK — Stamp Duty Land Tax
· FCA — checking an adviser is regulated

The amortisation, yield and depreciation formulas used here are standard published finance formulas, not proprietary methods — you are encouraged to check them against any other source.