How to Calculate Inflation-Adjusted SIP Purchasing Power

Put the ending value and payments on one price basis

A growing balance can buy less than its nominal number suggests. To compare gains fairly, express the ending value and each contribution in purchasing power at the start of the plan.

Nominal money and opening purchasing power

An inflation-adjusted SIP compares a fixed nominal monthly investment plan with its value in opening purchasing power. Both rates are user-supplied effective annual assumptions.

Opening purchasing power expresses an amount using the modeled starting price level. If prices rise, the same amount of nominal money buys less at a later checkpoint.

Compare inflation scenarios

Hold the contribution, horizon and investment assumption fixed. Compare zero inflation with a positive rate and a deflation scenario. These illustrations do not assign probabilities.

Inflation-adjusted SIP formula

For monthly investment factor f, monthly price factor p and n months, a payment C at index k grows to C × f^(n−k). Divide nominal ending value by p^n. Deflate each contribution by p^k and subtract that comparable contribution total to find real gain.

Real ending value = nominal ending value ÷ p^n

Reconcile a 12-month SIP

Invest 500 at the end of each month for 12 months with 12% annual effective investment return and 6% annual effective inflation. Nominal ending value is 6,323.25. Dividing by 1.06 gives 5,965.33 in opening purchasing power. Contributions in opening purchasing power total 5,814.40, leaving real gain of 150.93.

The nominal sum paid is 6,000. Subtracting that sum from the real ending value would mix price bases.

1. Enter 500, 12 months, 12% effective investment return and 6% inflation.
2. Choose end timing and compare the two ending values.
3. Subtract 5,814.40 in deflated contributions from 5,965.33 in real ending value.

Separate the rate from the gain

Compare monetary values on the same price basis. The nominal sum of payments mixes amounts paid at different checkpoints. The effective annual real rate is (1 + investment return) ÷ (1 + inflation) − 1 using decimal rates.

With 12% growth and 6% inflation, the annual real rate is about 5.660377%. Each payment has a different time invested, so this rate is distinct from total real gain.

Keep the payment fixed in nominal units

Enter a fixed nominal monthly amount, complete months, both effective annual rates and beginning or end timing. Compare terminal money with opening purchasing power, then reconcile real ending value and real contributions.

The currency selector only formats money. Enter an annual inflation scenario appropriate to the question you are exploring.

Choose the matching cash schedule

Use the SIP Calculator for a nominal monthly projection. Use the Inflation-Adjusted Return Calculator for a single opening amount exposed to a supplied price rate. An indexed contribution plan is a separate cash schedule.

Place each contribution at its checkpoint

The opening balance is zero. Beginning payments use indices 0 through n−1 and end payments use 1 through n. Each month is one twelfth of a model year. Fixed payments do not rise with inflation.

At end timing, the last payment is deflated across the full horizon but has no investment growth. A beginning payment receives an extra month of both investment and price exposure after payment.

Understand the scenario limits

Use up to 10^12 per contribution and 0 through 1,200 months. Rates must be above −100% through 100%, with up to 12 decimal places. Calculations use 100 significant digits and reject monetary totals above 10^30.

A constant price factor does not describe actual price changes. Personal spending patterns can differ from a published basket.

Avoid mixing money-year bases

Avoid comparing real ending value directly with a nominal sum of payments. Avoid subtracting inflation from return when you need exact compounding. Do not use an already inflation-adjusted return as the nominal input.

If the assumed rates are equal, each invested payment has zero modeled real growth after its payment date. Later contributions can still have less opening purchasing power when inflation is positive.

Use a local currency and a supplied assumption

Indian readers often use SIP and corpus. US, UK, Canadian and Australian sources commonly discuss purchasing power and inflation. Select INR, USD, GBP, CAD or AUD. The calculation does not import any country’s CPI.

Educational scope

Educational constant-rate scenario with no CPI lookup, actual dates, fees, tax, inflation-indexed payments, FX or forecast. It does not provide personalized investment advice.

Frequently asked questions

Sources and review

Sources reviewed Nov 10, 2026. Consult current local rules before relying on time-sensitive information.

• HDFC Mutual Fund SIP assumptions
• Investor.gov purchasing power
• MoneyHelper inflation guide
• Bank of Canada inflation calculator
• Reserve Bank of Australia inflation explainer