Free tool · Rent escalation
CPI rent escalation calculator: the adjusted rent, with a cap and a floor.
A CPI escalation clause raises the rent by the change in a consumer price index between two dates, often held between a floor and a cap. Type your rent, the index value at the base date and at the adjustment date, and any cap or floor, and this page shows the adjusted rent, the percentage change and the formula. You supply every number: the page has no index data, fetches none, and nothing you type into this calculator is sent.
Work out the adjusted rent
Enter the rent and the two index values, and choose a year or a month, to see the adjusted rent.
Arithmetic on the figures you typed. Your lease decides what the rent actually becomes, so check the result against the clause.
Nothing you type into this calculator is sent. Everything you enter stays in your browser: the calculation runs on this page, and the dates and numbers are not sent to us or stored. The page records the visit (which page it was and when, a random visitor id in a first-party cookie, the site or campaign you came from, whether you arrived through an ad click, and a mark saying whether the visit looked automated or came from our own team), where on the page you were when the visit began, whether you are still on the page after about five seconds and how far down you have scrolled by then, and any click on a button that leads to uploading a document ("Read my own lease", "Add a contract" in the header, or the bar at the foot of a phone screen), with which button it was (see Privacy). Nothing you type into this calculator is included. These records do not include your IP address or the name of your browser. The upload form at the foot of the page is separate. It records the kind of file you choose and a size band, never its name or contents, and that an account was made from it or an upload was started, finished or stopped (with which step and a short reason). The file and any email address you put in it are sent only when you submit it.
The formula
index change % = (index at the adjustment date / index at the base date - 1) x 100
applied change % = the index change, raised to the floor or held to the cap if you enter them
adjusted rent = current rent x (1 + applied change % / 100)The change is not rounded before it is applied. The adjusted rent is rounded once, to the nearest cent, with halves rounded up, and percentages are shown to three decimal places. If your lease rounds the index or the percentage first, round those figures as the lease says before you type them in.
Over the base rent, or over last year's rent
Leases differ on what the change is measured against, and the calculator does the same arithmetic either way: you choose by what you enter. If the clause adjusts the base rent by the change since the base date, enter the base rent, the index at the base date and the index at this adjustment date. If it adjusts the previous year’s rent by the change over the last year, enter last year’s rent, the index at last year’s adjustment date and the index at this one. Read the clause to see which it is.
Worked example
An example, not your lease: a rent of 4,000.00 a year, an index of 300.0 at the base date and 306.6 at the adjustment date. The index figures are made up to show the arithmetic; they are not real index values. Each row is this calculator's own output.
| Case | Change in the index | Change applied | Adjusted rent |
|---|---|---|---|
| No cap or floor | 2.200% | 2.200% | 4,088.00 |
| A 2% cap | 2.200% | 2.000% | 4,080.00 |
| A 3% floor | 2.200% | 3.000% | 4,120.00 |
The cap holds the 2.2% change to 2.000%; the floor lifts it to 3.000%. Where neither is reached the change applies in full.
Check these in your lease before you rely on the figure
The index, the area and the series
Which index the lease names, for which area or population, and which exact series. Use the series the lease names, not a similar one.
The base date and the adjustment date
The month the lease treats as the base, and the month it compares for each adjustment. Read which months the clause names, and use the index for those months.
What the change is measured against
Over the base rent since the base date, or over the previous year’s rent since the last adjustment. Enter the figures the clause uses.
A cap, a floor, or both
Whether each is a percentage of the increase, whether it applies each year or to the whole period, and whether the rent can fall at all.
How the index and the percentage are rounded
Some clauses round the index values or the percentage before applying them. This page does not round the percentage before it applies it; round the figures as the clause says before you type them in.
When the new rent takes effect
The adjustment date, and what happens if the index for the month is published late or revised.
What it will not do
This calculator does not know your lease or any index value. It uses the rent, the two index values, the cap and the floor you type, and nothing else. It does not decide when an adjustment applies, whether the rent may fall, or whether a cap is annual or cumulative, and it does not look anything up. Your lease decides what the rent actually becomes. It is not legal or financial advice.
Questions
How is a CPI rent increase calculated?
Divide the index at the adjustment date by the index at the base date and subtract one: that is the change in the index. Hold it to the floor and the cap if the lease has them, then multiply the rent by one plus that change. With an index of 300.0 at the base date and 306.6 at the adjustment date, the change is 2.2%, and a rent of 4,000.00 becomes 4,088.00.
Where do I find the index values?
The lease names the index and the months to compare. The figures come from whoever publishes the series, and this page does not fetch or store any. In the United States the Bureau of Labor Statistics publishes the CPI-U, the consumer price index for all urban consumers. In the United Kingdom the Office for National Statistics publishes the CPI. Use whichever series your lease names (for example CPI-W, CPIH or RPI), with the area and months it names, and look it up by name.
Does the increase compound?
That depends on the clause and on what you enter. If the lease adjusts the base rent by the change since the base date, enter the base rent with the index at the base date. If it adjusts the previous year’s rent, enter that rent with the index from a year ago. The arithmetic is the same: rent times one plus the change.
What does a floor of zero do?
It stops the rent from falling when the index falls: the change applied is 0%. Enter 0 as the floor if that is what your lease says. With no floor, a fall in the index lowers the rent in this calculation.
My cap is a yearly cap but I am measuring several years. What do I enter?
A cap and a floor here apply to the change over the period between your two index dates. If the lease states them per year, work year by year, with each year’s rent and the index at the start and end of that year. Read the clause.
How is the result rounded?
The percentage change is not rounded before it is applied. The adjusted rent is rounded once, to the nearest cent, with halves rounded up, and percentages are shown to three decimal places. The arithmetic is exact, not floating point.
Is anything I type sent to you or saved?
No. Nothing you type into this calculator is sent to us or stored: the calculation runs in your browser, on this page, and there is nothing to sign up for. The page does record the visit (which page it was and when, a random visitor id in a first-party cookie, the site or campaign you came from, whether you arrived through an ad click, and a mark saying whether the visit looked automated or came from our own team), where on the page you were when the visit began, whether you are still on the page after about five seconds and how far down you have scrolled by then, and any click on a button that leads to uploading a document ("Read my own lease", "Add a contract" in the header, or the bar at the foot of a phone screen), with which button it was (see the Privacy page). Nothing you type into this calculator is included. These records do not include your IP address or the name of your browser. The upload form at the foot of the page is separate. It records the kind of file you choose and a size band, never its name or contents, and that an account was made from it or an upload was started, finished or stopped (with which step and a short reason). The file and any email address you put in it are sent only when you submit it.
Is this legal advice?
No. It is arithmetic on the rent, index values, cap and floor you type, and it assumes nothing about your lease. It is not financial advice either. Before you rely on a figure, read the clause in your lease that sets it and, for a lease that matters, ask a lawyer.
Read more
The guide to rent escalation and CPI adjustment dates shows how the dates and rules are read from a lease. Prism lists the rent steps it finds, with the clause each one comes from, where one was captured; it does not look up an index.
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Try Prism on your own lease.
Prism reads a lease and lists the notice windows, options and rent steps it finds, each with the clause it came from, where one was captured. It can miss a date, so check the list against your lease. How often it finds them is on the accuracy page.
Read my own lease